[Duplo]

> I don't actually how much it costs to run a DHT node, or even who's paying for them today

By default all BitTorrent clients are acting as DHT nodes (if they can receive inbound UDP packets). You can disable it in the options, but most don't (unless for private trackers on per-torrent basis). I don't think anyone actually runs a DHT node like Tor exit nodes (except researchers and search engines like BTDigg).