We sell (err Adopt out ) stray kittens/cats. We sell them for $160 which covers desexing, microchipping, vaccinations, worming, de-fleaing etc. We don't make any profit whatsoever (we feed them, house them and look after them for as long as they are with us), as like most rescue places. The only difference is we only take in a max of 6 kittens to rehome so that they get our undivided attention.
However, having said that, I've recently heard that some shelters "buy" them from pounds at a reduced price (rather than selling them to the public) and sell them for a higher amount than what the animal would be sold for at the pound. That's wrong.