I have a theory about this actually. Do you have any specific data r.e. what "prices" were accepted?

My theory is that below a certain margin (I never tested this you see) then it becomes a different matter. At , say, £10,000 you are trading your body, it is transaction. You are gaining the money.

At a certain lower bound it switches to being simply an incentive. "I'll buy you dinner if you'll sleep with me after". i.e. it sweetens the deal.

I very much doubt that anyone, if offered $100 right here right now would take you up on the offer (but, then, I've never tested it)