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
Feats providing market price discounts
Except in the last case, each of the following feats provides the creature that possesses it a market price discount on magic items. The last feat must be possessed by the magic item's creator instead.
The Greyhawk regional feat Celestial Scion (Torquaan) (Dragon #315 52) "allows you a 10% discount on all purchases made anywhere the influence of House Torquaan is known," therefore applying pretty much wherever the DM says it does. Unlike the rules for regional feats in the Forgotten Realms campaign setting that were updated by the Player's Guide to Faerûn, Greyhawk regional feats can be taken by anyone who has a feat slot open and at least 2 ranks in a specific Knowledge (local), in this case one or more of Knowledge (Ablissa, North Kingdom, or Solnor Compact local). Still, this feat is limited to 1st level characters.
The general feat Favored (criminal guilds) (Cityscape 61, 87) gives a creature a 5% discount on magic items the creature purchases from the guild, but a particular minor magic item is available only 50% of the time, a particular medium magic item only 25% of the time, and a particular major magic item only 10% of the time. When the guild's inventory is updated is unmentioned by the text; ask the DM. Also, goods purchased through the criminal guild are illegal or stolen, and this can be a problem.
The general feat Favored in Guild (Complete Psionic 51) for the criminal guild Gnawbones (Waterdeep: City of Splendors 56–7) or the special guilds the Harpers (73–4) or Tel Teukiira (75–6) allows the character to purchase a magic item with a market price of 50,000 gp or less at 75% of market price… once per character level.
The Forgotten Realms regional feat Mercantile Background (Player's Guide to Faerûn 41), among other benefits, allows a creature to, "[o]nce per month,… buy any single item at 75% of the offered price." It is available to 1st-level dwarves from the Sword Coast or the Darklands section of the Underdark; gnomes from Lantan or the Northdark section of the Underdark; halflings from Amn; and humans from Amn, the Lake of Mists section of Hordelands, Lantan, Sembia, Tashalar, Tharsult, Thesk, Turmish, the Vast, or Waterdeep, or as a Shou Expatriate.
The ceremony feat Ritual Transference (Player's Handbook II Web enhancement "Magic Items: Transferring XP Costs") in its Special, in part, says, "If you are commissioning the creation of a magic item from an NPC with this feat (for which you are providing spells), a discount consistent with your contribution and type of magic item is subtracted from the final market price (see Table 7-33: Estimating Magic Item Gold Piece Values, page 285 of the Dungeon Master’s Guide)." Thus a creature can commission a magic item from a creator who possesses this feat then help that creator create the commissioned magic item by casting spells. Doing so entitles the creature to a discount on the commissioned magic item's market price.
This is the best way of getting a market price discount on magic items, but this way does require pretty much moving in with the creator while the magic item's being created and casting spells to assist in the magic item's creation. Further, the DM may not have incorporated these obscure rules into the campaign setting.
Skills
Organizations
Note: It's unlikely given its provenance that the DM will allow the feat Guild Discount (Planewalker Web article "Guild Discount"), and it's pretty specific anyway. Thank you, Peregrine Took, for having me look at Complete Adventurer. Thank you, Prevarications, for the suggestion of the feat Mercantile Background.