If my husband approached me with that kind of proposal, that would be grounds for divorce IMO. The kind of man who would be willing to actually sell me for cash would be willing to do a whole lot of other things for cash, and I am not trying to grow old with that kind of fool.
If I found the man attractive and charming, and would have otherwise done him for free if I wasn't married, I would go ahead and do him. Then I would arrange for the man to convey the money to my mother, rather than me, so that when I sue my husband for divorce, my husband cannot see a red cent of that money (it can't be factored into my worth and considered marital property). Only after the divorce would my mother convey the money to me (I trust her and only her like that) for me to enjoy husband-free.