Regeneration + Mitigated-Unhealing based on Number of HP Regenerated?

[watsonsword]

Making a character who's body contains a reservoir of substance it can use to heal itself. When this substance runs out, the character can no longer heal until this substance is replenished.

I thought I could do this by combining regeneration and minor-regrowth with total-unhealing. The total-unhealing would have a treatment-mitigator. This treatment is not based on time, but on number of HP regenerated. The character can only regenerate X HP before total-unhealing activates. It then deactivated with treatment.

Thing is, with my current sources, there's no way for me figure out what the point cost would be!