I like the substack model, in order to comment you must be subscribed to the newsletter (say $5 per month), while others can read the article and comments.
Unfortunately a lot of people are quite happy to pay to post absolute nonsense online, because it's their only outlet and makes them feel validated.
I don't know if that's the best method though. If some PAC decided it was going to pay for the subscriptions of its members as a campaign, then that subscription model isn't really a big barrier.
I’d imagine that’s substantially less common than your everyday racist spambots in news comment sections. I doubt the amount of influence you can gain from astroturfing a news comments section is worth the cost of dozens of newspaper subscriptions.
But are the owners of spambots going to pay subscription fees for their bots?
And most news papers already have a login for paid subscribers. Seems like a nobrainer. Certainly will attract less bot spam if you need to be a paid subscriber.