Pricing of items with triggered spells?

[Garloth]

Hello.
Say I want to make a ring that, when my hp drops below 0 cast Cure Serious Wounds on me.
The pricing for the spell would be doable, but what about trigger?
Neither I nor my DM has any idea.
Any resource on that?

[Kelb_Panthera]

Off the top of my head, add a contingency spell effect as part of the cost.

CSW is a 3rd level spell times cl 5 times 2000gp for use activated makes 30k divide by 4 (ad-hoc) for an odd trigger condition makes 7500

Contingency is a 6th level spell times cl 11 times 2000 for continuous effect times 1/2 for duration makes 66000

Total is 73500gp by my estimate.

However, I think that such an item already exists at a much cheaper price, though that device was limited to once or twice a day IIRC.