I used to feel like that. I think it boils down to:-
(1) You've just thrown away £xx for x mins "entertainment". Think of ways other people blow their money: drink, gambling, sports cars, etc.
(2) You feel like a walking ATM. The steps leading up to that feeling are: Girl says she is looking forward to sex with you, girl screams with ecstacy at every thrust, girl puts on clothes and says "right who's next please?".
Look for a regular who is prepared to give you some individual treatment: not just a number on her mobile. Small things like she remembers your name, things you like, etc.