That makes a lot of sense. Taking it further, you could also introduce a sliding scale for comment volume, like $1 for <10 comments/mo, $5 for up to 30 comments/mo, or the $100 "troll package" for up to 80 comments/mo.
It doesn't even need to be that fancy in practice. It's just the simple fact that you now have to pay real money, even a trivial amount, to contribute to the discussion that keeps out a huge amount of low quality content. It also disincentivizes bots and abuse (too costly), and can help with serious threats/issues as there's a paper trail to some payment processor somewhere should authorities ever need to get involved (not that there aren't ways people get around that, but it's just more speedbumps against trolls).