Only me selling:
An amount high enough that it does not feel insulting. I might get more use out of $0.95 (hey, that's an apple at the supermarket) than my one vote, but frankly the offer's a bit offensive. $50 would probably do, that's gas for a month.
Mmm, depends. Ignoring the option of, say, moving to a swing state, and selling it before a major election... eh... Several thousand. Probably nobody would buy at that price, but, eh, whatever.
Though I must say, the latter situation sort of sounds like a libertarian dream. But, maybe that's just my cynicism talking.