If you say that the whole point was to provoke people to think, and not to glean any information about what they would actually do, I'm fine with that. However, I'm skeptical that women would devote much thought to the imaginary situation that will never happen when they were in a real situation where they were being asked to discuss their sexuality. It's kind of like you've never seen or heard a goat before, so you walk up to someone with your pet tiger on a leash and ask them to do an impression of a goat. You're going to get an impression calculated not to excite the tiger, without much thought to what a goat looks and sounds like.
I'm actually most interested in your currently undefended assertion that people have thought about their "price". It's the most interesting part of this for me.
As a kid I had multiple conversations in different groups of guys where the question of having sex with another guy for money came up, so I think I can vouch for guys. Even in groups of guys who weren't particularly intimate and didn't trust each other, you'd get exchanges like, "Dude, you are so in love with that guy you would suck his duck." "Fuck you, I'm not sucking anybody's dick." "So you wouldn't even for a million dollars?" "You saying you wouldn't? What are you trying to hide?"
As for girls, girlfriends have told me about giggly conversations they had with their friends when they were thirteen. The question naturally arises from the question of whether you would marry a gross old guy who had billions of dollars -- and that's something that all young girls talk about. It's an irresistible mixture of horror and fantasy. Start altering that story and you're only two or three steps from outright prostitution. (Amusingly, in the one story I remember pretty well, the question posed was, "Would you have sex with a guy for a million dollars, even if you didn't love him?" I guess to thirteen-year-old girls, love is the factor that makes everything okay or not okay, even prostitution.)
Another reason is how people reacted to the movie Indecent Proposal with Robert Redford, Demi Moore, and Woody Harrelson. It wasn't an alien idea for most people. Anytime people talked about it, they seemed to be picking up the threads of conversations from a long time ago. Of course, people are a lot less likely to talk about it with people they don't trust, especially when the intent seems to be hostile or transgressive.
