Metafilter is an interesting case - it costs $5 to sign up. It’s a very civilised place (although not entirely without its problems) and I think they hold that this nominal sign up fee is a big part of that - less spam, fewer drive-by miscreants.
Other than that, the OP proposal smacks to me of ‘one dollar one vote’ and that idea fails in part because the value of money varies extremely widely between different people.