Usenet thrived in a time where most of us trusted each other, traffic was an order of magnitude lighter, trolls were few, spam was unheard of, and moderation - if any - was cheap and painless. I honestly believe those times are past us. And I say that as someone that loved Usenet back in the day. What you're asking for, for free , isn't possible.
Wasn't that sort of included in your Internet subscription?
Even if not, why not use the same model as Internet subscription, where the payment comes from the fee you pay to your ISP? This would also make it easy for governments / donors to sponsor participation in such groups as they wouldn't have to hunt down individuals to provide them with a tiny amount of money, rather they could compensate ISPs directly.
A lot of ISPs are trying to make some extra $ by selling all sorts of junk, like anti-virus or w/e. Sure they wouldn't be opposed to sell an extra service, should it become popular enough.