In my Navy days I knew a Warrant Officer who insisted there were only two categories of sex...and that you paid for both.
The first category was "commercial" sex with a straight-forward fee. The second category was "all other" sex which was finaced with a value added tax.
His views on the relative return on investment were rather interesting ;-)
And he's right.....no such thing as free, errr, kitty. In the end everyone pays but men more so than women.