How much do female mainstream porn stars earn per scene? [closed]

Not sure exactly what you mean by "mainstream porn star." Porn actors (both male and female) are generally not, or at least no longer, "mainstream."

Also, porn is, generally speaking, a cash business with scenes being filmed not in studios, but rather in homes and hotel rooms, and not in any of the mainstream studios. Of course, there are a few full on studios, used by production companies that have grown enough to warrant them, but the large majority of "porn production" is back room, cash, under the covers (no pun intended, really) operations.

Porn production has not unionized, by and large, and porn actors, generally speaking, are not members of the Screen Actors Guild and are not covered by their collective bargaining. So their pay scales are not published and not set down on paper. The pay for a scene is usually whatever the actor and producers agree it is.

All that aside, yes, it is kind of common knowledge that certain scene types demand more pay, due to their distance from the 'norm', whatever that is. Scenes could be (very, very generally) viewed as increasing in salary levels, such that, from low-ish to higher pay might be found in: boy-girl, interracial, homosexual/gay/lesbian, bi-sexual, then levels of Bondage/BDSM/Pain. Also take in mind that the more 'risky' a scene is to the health of the actor, the more the production would be willing to compensate.

Risks depend on many things. External physical, from bondage, whipping, spanking to needles, etc. Could also be 'internal' physical, such as bareback bisexual with passing of STDs, HIV, etc.

Of course, since porn actors are not "mainstream" and not protected by something like the SAG, then each stars ability to command pay is dependent completely on the producer's willingness to pay them. Porn is notorious for being the "wild west" of film-making. i.e., if a porn actor needs to eat, then she's more likely to take whatever work she can get.