First off I would NEVER use Craigslist too find a home for an animal, too many animal brokers lark there.
As to a fee most shelters and agencies I work with charge from $ 100 - 200. per cat. Higher for pure bred kittens and lower for older. This also eliminates the animal brokers. Some even require you to bring the animal in 2-3 months after adoption. Just so they can be checked.
Over the last 8 weeks I have moved 37 cats & kittens, including 1 EX grand champion. So far all have been placed except 2. I have even meet some of the adopter’s.
All I can say is be very careful.