Instead of paying trolls, monetizing trolls might be a good idea. You could have people buy karma, buy mod rights, buy out other people's mod rights, etc.
Of course posting and downvoting would have a karma cost.
- this assumes that there would flood of users on this site and a chunk of them will actually pay for it. Will you use HN if there is a fee? Instead, why not just write an algorithm to limit spam Or a 'report spam' button?