Vestige-less Binder ?.......

[nonsi]

What would you suggest as possible "prices" from the patron?

I'm guessing it should have a lot to do with the nature, personality and agenda of the patron:
- ability corruption
- signs/markings
- deformities
- vulnerabilities
- numeric penalties to combat stats
- always detected as evil / all spells gain the evil descriptor
- taboos
- human sacrifice
- OCD
- phobia
- assignments (soul collection, religious preaching, raising temples, eradicating a city/nation/culture...)

This can basically go anywhere, but the various prices should be of relatively similar costs and not something that would make it problematic for the character to go about his business.