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.

Yes.

The phrase "including X" means that X is not a comprehensive list of effects.

The only way for Suggestion to not be stopped by Protection from Evil would be for Suggestion to not qualify as an attempt to "exercise mental control over the creature." I doubt such an interpretation exists.

For what it's worth, I believe the reference to charms, and compulsions that grant ongoing control is an intensifier clarifying that Protection from Evil will suppress spells that have already been cast on the target but are still in effect. The examples given (Charms and Compulsions) both fall into the category of long-term mental manipulation.

It is likely that at some point play testers were confused about the interaction between spells like Dominate or Charm Person and Protection From Evil, so they added an aside to address them. Asides like that aren't meant to be all-encompassing, they're simply a way of saying "yes, even these."

Appendix: English Fun Time

As with many bits of rules text, this can be interpreted several ways. The way I'm interpreting it is simply the one that strikes me as following the written text most closely, while leaving a minimum of unknowns.

There are other interpretations that are valid from an English syntax point of view, but generally leave lingering questions. Whether these interpretations are better, worse, valid, or invalid doesn't concern me here. Only whether my interpretation fits the printed text.

Okay, so let's strip down Protection From Evil to a more streamlined version that's a bit easier to talk about:

This spell blocks any attempt to exercise mental control over the target, including effects that grant the caster ongoing control over the subject. The protection suppresses the effect for the duration of the Protection From Evil effect.

I've italicized the controversial bit. The phrase "exercise mental control" isn't defined in the game, so you have to pick an interpretation. There are three reasonable ones:

• An attempt to exercise control is an action that imposes a condition on a target that forces it to act in a certain way. E.g. casting the Dominate Person spell.

• An attempt to exercise control is an action that gives a target a new compulsion. E.g. issuing a command via Dominate Person.

• An attempt to exercise control is anything that overrides the will of a target.

You can take your pick. The first one causes the "but what's this clause for?" problem, but both of the second two line up.

For my part, I choose the third interpretation, because it feels closer to natural language, and I don't like adding rules constructs without purpose.

Let's look at an example. Say I give you a Suggestion, and order you to dig ditches until the spell ends (in 10 hours). Three hours later, the English sentence "I am exercising mental control over you" is a valid statement. Even though I'm not actively issuing new commands.

Now suppose someone casts Protection From Evil on you (and we suppose it works the way I say it does).

The English sentence "I am attempting to exercise mental control over you, but it is being suppressed by Protection From Evil" is a valid sentence, that is in agreement with the text of the spell.