As you can see from my forum profile at another SMF discussion board I frequent
(<-link), I am a "subscriber," ie, I pay a certain amount a year from my poor student budget ($50) to support the board. Subscribers get pretty much no perks beyond a giant PM inbox and a little icon under their names. There's no prestige boost associated with these and I honestly have no clue who else is a subscriber because I never look.
Now, the other board I visit has running costs of $2000/yr rather than just $475/yr. But I think our community here at WNFF is devoted and close enough that if, for example, the "Subscription" option was ten bucks, you'd have enough people volunteer, out of sheer goodwill and love of the forum, to knock that price down by half.
I do get the banning issue, though. The forum I linked to above is about classical music, and since we're all nerdy old geezers who play Bach all day
, only one person has been banned in the last 3-4 years. (Two more got warnings and one crackpot who was trying to convince us that Mozart was a hoax voluntarily left after everyone, including management, begged him to.)