"In your examples of individual scenarios above, if a woman is so desperate for money she will do anything (needs food, to pay the rent, drug addiction etc) is it ethical for a man to exploit that desperation for sex?"
I am sorry but this victim scenario does not work. We do not live in a world anymore where women have no possibility of income. In fact, did you see the recent article in The Economist? For women at the same level, function and company, the gap is now only 0.8% and overall 26.8% (Germany btw only 15% as it is much less unequal than Britain meaning the gap between the low earners, more women, and higher earners, more men, is smaller. Interestingly, the gap for same function/level/company is higher in Germany which from a solely public/media based perspective seems true, Germany seems to lag Britain in terms of gender equality initiatives at the high level).
Anyway I digress, I made a hypothetical, and you changed the hypothetical. The ten million part was clearly to show, she isn't doing it to survive, but the sheer amount of money - and let's face it, there will be women who aren't prostitutes who would do it for that much money.
It's actually quite telling that you categorically view prostitutes as victims (of circumstance). Not denying that most are, I am sure that many would scoff at your opinion of them as victims. And maybe simply because you would never do something like that other than if you had to to survive, doesn't mean that all women think like you. I think we can agree that for men, many would do it. And why can't some women be more like men in this regard than most other women? I don't know, but in my opinion, that is not unreasonable at all.