I think the majority of answers are going to be predictable , most of the guys would jump at the chance of being paid to have sex but they would put provisos on it such as she can't be over a certain age or the like.
Whereas the most girls are more emotionaly in touch with their sexuality and it represents more to them so they will most likely say no, (with the exception of maybe a couple).
Personaly I have sold myself once.
A (girl)friend of my girlfriend paid me Ā£20 for a kiss in 1988.