By the book (SRD):
With regards to the formulas:
Not all items adhere to these formulas directly. The reasons for this are several. First and foremost, these few formulas aren’t enough to truly gauge the exact differences between items. The price of a magic item may be modified based on its actual worth. The formulas only provide a starting point.
With regards to creating woundrous items:
To create a wondrous item, a character usually needs some sort of equipment or tools to work on the item. She also needs a supply of materials, the most obvious being the item itself or the pieces of the item to be assembled. The cost for the materials is subsumed in the cost for creating the item. Wondrous item costs are difficult to formularize. Refer to Table: Estimating Magic Item Gold Piece Values and use the item prices in the item descriptions as a guideline. Creating an item costs half the market value listed.
So it is suggested BTB that you use the formulas as a starting point, but base the actual value on worth and in comparison to other comparable items.
Now, this is how I would do it.
My assumption is by the time Heal is available, low level healing spells find much less use in combat. Low level spell slots also become less useful for other spells, thus freeing them up for healing. Thus at 11th level (minimum casting level for Heal), unlimited out of combat healing is still very useful but less so than prior. I would price out the item at half of the expected wealth of a 11th level character (66,000gp off the top of my head) to give a final price of 33,000gp. This would be for a unlimited use, CL1, CLW item. Most likely all the characters would pool their money for this purchase, making it easier to pay for.
By the time Mass Heal is available, this item will find far less usage and should be worth no more than about 5-10% of a 17th levels expected wealth. I don't have my book in front of me to confirm if this works out or not.
What other items could the characters purchase for 33,000gp?
33 x Pearls of Power (Lv1) which gives 33 x CLW each day at the clerics own caster level and gives greater overall flexibility (it can be use to regain other 1st level spells expended)
or
44 x Wand of CLW (CL1, 50 charges each) = 2200 charges of CLW. I estimate this would be enough healing to last for anywhere between 5-8 levels depending on how much other healing is available to the party.
If spells like vigor are available in the campaign that give a higher hit point per spell level recovery rate, their is some way to recover unlimited hit points up to 50% of maximum (such as the Dragon Shaman aura or one particular reserve feat), then I would price the item out somewhat lower, perhaps as low as 20,000gp.
Hope this helps!