Of course this leads to the question: if voting has a cost, then how do people accumulate irrespective of themselves receiving a vote?
You could give everyone say, a fixed number of karma to begin with that could then be allocated. You can then give people more karma for successfully being a user without being flagged or receiving certain amounts of negative karma for a time period.
It's a shame there's not more experimentation here. This could lead to more interesting sort of dynamics. For example, if the #1 person believes something is being said that is really damaging in some way, they could put at stake the entirety of their karma and downvote it, which would pretty much obliterate the comment. Conversely, if someone is speaking a truth no one else is acknowledging someone with a lot of karma could sacrifice a good chunk to bring it right to the top.