Yes, for D&D 3.5 the Pathfinder Adventure Path "Curse of the Crimson Throne" deals with a plague in the city of Korvosa and they've published some various rules for diseases and plagues. Specifically, Seven Days to the Grave has an article entitled "Plague and Pestilence: Diseases of Fantasy and Reality", which besides having diseases and gear relevant to diseases has some treatment of larger scale plagues (outbreaks, epidemics, and pandemics). Then they updated those rules to Pathfinder as part of the Affliction rules in general and added a lot of real-world tropical diseases in the recent Heart of the Jungle supplement.
And lucky for you, a lot of that has found its way into the Disease section of the Pathfinder SRD!
Here's how it works, I'll illustrate with my favorite sample disease, dysentery.
Dysentery
A broad family of intestinal
afflictions caused by everything from
bacteria to viruses to parasitic
worms, dysentery is characterized by
explosive and sometimes bloody
diarrhea, leading to dehydration and
occasionally death.
Type disease (parasite), contact or
injury; Save Fortitude DC 16
Onset 1d3 days; Frequency 1/day
Effect 1d6 nonlethal damage and target
is fatigued and staggered; Cure 2
consecutive saves
This means that when you're exposed you have to make a Fort save DC 16 or else you get the disease and it manifests symptoms in 1d3 days. You make a new save every day once it manifests and if you fail you take 1d6 nonlethal and are fatigued and staggered. You have to make 2 consecutive saves to get better; with this one it doesn't run its course otherwise.
Contextually, Bob's correct
If the campaign is a series of tombs of horrors, then that ring of cure light wounds is an item beyond price. If the party can't leave the dungeon to resupply and can't get down to one encounter per day (i.e. the so-called 15-minute workday) via spells1, that ring of cure light wounds is a literal lifesaver.
In other words, if the campaign is already on hard mode, the ring switches it not to easy mode, certainly, but to average mode. That's a legitimate concern for the DM. The DM's already decided the campaign's supposed to be difficult and the ring makes the campaign substantially less difficult. As the ring violates a central campaign tenet, the ring just shouldn't be available… or only available as a result of a heinous Gygaxian Faustian bargain.
For the game as it was likely envisioned, Erin's correct
The Dungeon Master's Guide would likely pick Erin's suggestion. If worry-free, constant healing is desired, everybody should pony up for rings of regeneration (DMG 232) (90,000 gp; 0 lbs.). Sure, each ring of regeneration costs as much as 120 wands of cure light wounds [conj] (PH 215–16) (1st-level spell at caster level 1) (15 gp/charge), but, y'know, the Dungeon Master's Guide says to "[u]se good sense when assigning prices, using the items in this book as examples" (282), and the ring of regeneration presents the example of the price of worry-free, constant healing, so that is the price of worry-free healing. In fact, an original magic item like a use-activated ring of cure light wounds—like a continuous item of true strike [div] (PH 296)—is such an anathema, I'm willing to bet were the year 2000 Dungeon Master's Guide a DM that it would laugh at the player who suggested a ring of cure light wounds and maybe have the next wandering monster attack him first just for asking.
For many games as they are now, Alice or Dave is correct
Many current players feel that constantly reacquiring wands of cure light wounds to have their characters freshen up between encounters is, at worst, a mere inconvenience, like tracking how many arrows remain in a quiver. In the same way that being short on arrows creates tension at low levels, managing healing resources at low levels creates tension. Many players, though, feel that by the time a character's reached a reasonably high level—say, 9 or so—that the character should have more important things to worry about than how many arrows he has left, and he shouldn't worry that he's burning party resources because he fell down a 200-ft.-deep pit. A Ftr9's Wealth by Level (Dungeon Master's Guide (203) 135) says that a wand of cure light wounds—that is, an entire wand, fully charged—is only about 2% of the gear he's toting. Seriously, after splitting four ways the take from a lone level-appropriate encounter, a Ftr9 can buy a whole new fresh wand of cure light wounds and still have gp left over.
If a DM has players like Alice and Dave, a ring of cure light wounds makes the game more fun because it cuts down on tracking charges from wands of cure light wounds, and the DM should probably allow it—either at low levels at Alice's price or higher levels at Dave's price—unless the DM's vision of the game differs substantially from that of the players' vision.
A brief history of the ring of regeneration
As the sole item that grants continuous healing in core Dungeons and Dragons 3.5, the ring of regeneration is terrible and using it as an example of what continuous healing should cost is terrible. I'll explain.
Building as they were in 2000 from Advanced Dungeons and Dragons, 2nd Edition, the ring of regeneration included in the Dungeon Master's Guide for Dungeons and Dragons, Third Edition probably looked fine to the original core rules' authors. The changes made to the ring of regeneration were a much needed nerf to improvement over Advanced Dungeons and Dragons, 2nd Edition's ring of regeneration, which, for the record,
restores 1 point of damage each turn [10 minutes] and eventually replaces lost limbs and organs. It will bring its wearer back from death…. Only total destruction of all living tissue by fire, acid, or similar means will prevent regeneration. Of course, the ring must be worn, and its removal stops the regeneration process.2 (Encyclopedia Magica, Vol. 3 993)
Such an item was highly coveted in both Advanced Dungeons and Dragons (where it functioned similarly) and Advanced Dungeons and Dragons, 2nd Edition, and for good reason. One's character could lose limbs and organs. ("Why, hello there, sword of sharpness!") Dying was really painful instead of the speed bump that it typically is in Dungeons & Dragons, Third Edition. And healing was, itself, extremely valuable, the province of classes that often weren't much fun to play and rarely advanced beyond level 6 through actual play.3
So when the time came to include the highly-sought-after ring of regeneration in Dungeons and Dragons, Third Edition, the price was set very high because legacy yet the ring's actual functionality plummeted. Creatures no longer lost limbs except under extremely rare circumstances. Creatures now healed their levels or HD in hp per 8 hours rest instead of just 1 point per day of rest. And gone was the jazz about the ring bringing the wearer back from the dead. The only improvement Dungeons and Dragons, Third Edition made to the ring was proportionate healing (that is, Third Edition's heals a creature's level in hp)… and then Third Edition multiplied the ring's healing increment by 6.
Anyway, the current ring of regeneration seriously sucks as useful measure by which to gauge unlimited healing.
1 By, after the first encounter, hiding in, for example, the space created by the 2nd-level Sor/Wiz spell rope trick [trans] (Player's Handbook 273), the 5th-level initiate of Gruumsh (CR 24) spell pocket cave [conj] (Champions of Ruin 33), or the 7th-level Sor/Wiz spell Mordenkainen's magnificent mansion [conj] (PH 256).
2 Okay, a similar means to fire is heat. Sure. I get that. That's a thing. But what's a similar means to acid except, like, better acid? I hope whoever wrote that spent his $0.10 from those words wisely.
3 I find the experience level chart for the cleric or priest, respectively, in Advanced Dungeons and Dragons or Advanced Dungeons and Dragons, 2nd Edition—when compared to classes' experience level charts—hilarious.
Best Answer
The vigor spell line in Complete Divine and Spell Compendium is your go-to in 3.5. The line consists of:
They each last 10 rounds (one minute) plus a number of rounds equal to your Caster Level. There are also the 3rd-level mass lesser vigor and 6th-level vigorous circle for group healing, with Fast Healing 1 and 3 respectively.
Lesser vigor, in particular, is a 1st-level spell that is the most efficient HP-by-spell-level option in the game, healing 11 HP at CL 1. Therefore, wands of lesser vigor are pretty standard adventuring gear for folks “in the know:” it’s the most HP for your gold piece you can get.
In Pathfinder, the 1st-level infernal healing spell is nearly equivalent to lesser vigor (it lasts only one minute, rather than one minute plus CL rounds). However, strangely enough, it is [Evil]; this makes it harder to use as “standard adventuring gear,” but for healers who don’t mind the alignment issue, it’s still the best option. There is a celestial healing spell that is [Good], but it has a massively-reduced duration that makes it basically worthless. There is also a greater infernal healing and a greater celestial healing which work like greater vigor (Fast Healing 4), but are 4th-level instead of 5th-level. There are no group-healing options among celestial/infernal healing spells.
The difference in duration means that a wand of greater vigor is more cost-effective than a wand of greater infernal healing, but it costs more up-front, requires a higher-level crafter, and takes longer to heal. The point is largely moot as lesser vigor and infernal healing are both much superior in that regard, though. The duration on both celestial healing and greater celestial healing makes them worthless.
And then there is song of healing for bards, which grants fast healing 2 as a 4th-level spell to up to 3 targets. Considering it costs a 4th-level spell slot and only works in conjunction with a bardic performance, you would be better off just leveraging your Charisma to Use Magic Device some wands of lesser vigor.
Better, but still not good, are the 2nd-level path of glory and its 4th-level greater version. Both let you pick 4 squares when you cast, and add 4 more squares each time you use a swift action to expand it. Allies that end their turn in these squares heal 1 hp (or 5 hp for the greater version). So that works out to 1 (5) hp/round for at least four people, and potentially a lot more. In the best case scenario, this heals 4 (20) hp in the first round, then 8 (40), then 12 (60), and so on. At higher caster levels, that can be enormous—but it’s spread out among many allies. For a party of four, a minimum-CL 3rd path of glory heals 12 hp—that’s 2 hp more than infernal healing, for 6× the cost. Greater path of glory can’t even be gotten in a wand, and a minimum CL 7th scroll of greater path of glory costs almost as much as an entire wand of infernal healing. Best case scenario, it does heal 140 hp—but that’s still a rate of 0.2 hp/gp, where a wand of infernal healing has a rate of 0.73 hp/gp. And that’s if your entire party is hurt, and hurt badly enough to use the full healing.
Path of glory does have a synergy with the celestial totem rage power, which a skald can give to the entire party. A skald also casts bard spells, which path of glory is, so that’s convenient. Healing CL+1 hp/round instead of 1 hp/round is a big deal when you can put it on the whole party. However, the only reason this works is because path of glory isn’t technically “fast healing”—if it were, celestial totem wouldn’t work, because that rage power specifically blocks fast healing for exactly this reason. I imagine many GMs would therefore nix this combo.