Pornstars may earn6-figures annually....
But. I would guess that the average porn girl in the US gets paid a couple hundred bucks cash per scene. (Maybe 100$ or so in Eastern Europe...why do you think so many movies, even by US production houses are made there? It's not for the cheap hotel rooms alone...)
So, sure a Vivid/Wicked girl may earn a nice living. But the real cash is kept a long way away from the "talent". Most producers know that the average girl has a very short lifespan in the biz for 1.her own reasons and 2.she has a short shelf life.
Really, imo, it is not much different that a garage band getting signed and releasing one album that gets marketing support for one track....
The top girls, of which I am sure there may only be a dozen or so, may make a bit of dosh under "studio" contract, but I am sure a nice suppliment from their websites and merchandising.