I did it once as a boy. I got paid $50, but I had to bring a pair of men's underwear to the set, of which I had none. So make that a $40 profit. That money came and went, but those photos are forever. I don't mind.
About six months after starting hormones, a friend did a topless photo shoot of me for an upcoming book he's putting together about disenfranchised members of the LGBT community. He thought it was neat juxtaposing my breasts and my femininity with my then-broken wrist in a cast. This shoot was for free, because not only is he one of my very best friends, he also let me stay at his house for a month and a half when I had nowhere to go!
And I just noticed that both photographers are gay men. Go figure.