photo shoots and even j/o videos isn't really g4p. Gay For Pay really means otherwise straight guys escorting. Like in the straight world, escorting can mean anything from accompanying someone to an event to full fledged prostitution.
for top level bodybuilders, g4p is at least posing while the client jacks off. but usually there is more involved.
a national level competition bodybuilder should be able to make $500 for a one hour session. then there are the high price escorts, like the late Rob Sager, who'd fly to some city most every weekend to spend 3 days with a client for $4k and up.
and while there are some (often closeted) guys who pretty much only have sex with escorts, most gay guys have never paid for or been paid for sex.
Back to the videos, if you have a physique similar to what you find on musclehunks and powermen, you can make $5k and up plus an all expense trip to some exotic location. all you have to do is j/o once a day for 5 days in front of a camera crew.