Depends on the price. I'd have to think hard what my minimum would be. It would be a lot.
In practical terms my right to vote is pretty useless to me because I don't live in a swing state in the US and my UK constituency is a safe Labour seat, so the result will be the same whether I vote or not, so I don't.* So logically I should set the price at a few quid or dollars, but there's more to it than that. I don't know what more to it there is, but there is.
* I might vote if they allowed negative voting. But there's usually nobody I want to positively support, and voting for them would just encourage them when I think they all suck. Actually I'm not allowed to vote in the US until I've done my citizenship ceremony, so I can't sell what I don't yet have. And as they've never let me vote, I've not thought much about whether I would or not. The US is a bit less "first past the post" than the UK (I think), so my vote in the US might make a tiny difference, but it would be incredibly diluted. More thought required.
It might lead to something horrible if everybody did it, but not everybody would do it unless the money they were offered was going to set them up for life, and that's not going to happen.
Like somebody here said, who's making the offer, and what are they up to?
It's a bit like "Indecent Proposal" isn't it?