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.

It's Caster Level 8

Your second interpretation is correct. Here's the rule itself:

Creating a magic weapon has a special prerequisite: The creator’s caster level must be at least three times the enhancement bonus of the weapon. If an item has both an enhancement bonus and a special ability the higher of the two caster level requirements must be met.

Then from the Magic Weapons page:

In addition to an enhancement bonus, weapons may have special abilities. Special abilities count as additional bonuses for determining the market value of the item, but do not modify attack or damage bonuses (except where specifically noted). A single weapon cannot have a modified bonus (enhancement bonus plus special ability bonus equivalents) higher than +10. A weapon with a special ability must have at least a +1 enhancement bonus.

From here, it's pretty clear that enhancement bonus and special abilities are distinct things. You combine them for the weapon cost (as the rule stats), but not for the crafting caster level requirement as each type has its own requirement. You just have to be able to meet all the requirements.

Thus, you need CL 6 (3x2) to make a +2 enhancement bonus, and CL 8 (and have access to the spells Chill Metal or Ice Storm) for Frost.

This also means all the weapons on the chart can be created without being epic level, as if you needed to be CL 9 to make your +2 Frost Weapon, it'd be impossible to do any combination that is >= +7 without epic levels. (You can't make a +7 sword without epic levels, but you can make a +5 Keen Frost one, which has the cost of a +7 equivalent weapon.)

It Could Be Caster Level 6

Depending on how you want to interpret the rules around prerequisites, you could create the weapon at CL 6 as a Druid (who get access to Chill Metal at level 3). The reason for that is these rule passages. From the SRD:

While item creation costs are handled in detail below, note that normally the two primary factors are the caster level of the creator and the level of the spell or spells put into the item. A creator can create an item at a lower caster level than her own, but never lower than the minimum level needed to cast the needed spell.

And from DMG p. 215:

For other items [besides potions, scrolls, and wands] the caster level is determined by the creator. The minimum caster level is that which is needed to meet the prerequisites given.

Depending on how you read this, the prerequisite could only be access to the spell itself, rather than the CL listed. In that case a level 6 Druid could create the item (as they can do both +2 and have access to a required spell). A Sorceror would need to be level 8, as that's when they get access to Ice Storm.

I'm not 100% convinced this is how they intended it to work, but it makes an item entry like Universal Solvent make a lot more sense. It has a listed CL of 20, which for such a common an inexpensive item just seems really wonky if only the greatest spellcasters on the planet are able to create it (particularly since the required spell is available to Wizards at level 9).

If you use this interpretation, the CL listed on the item entries is a guideline, or what you'd expect a normal item of it's type to be if you find one in the world.