I have 0 doubt in my mind that it could cost 1 dollar and most people wouldn't pay.
"People won't pay" is absolutely fine for users who simply need a barebones systems and never need a priority ticket re a Postgres issue, or a priority update.
I actually think its fine to create two classes of users -- those that pay a modest amount, and those that pay nothing. Perhaps the lesson is those that pay a modest amount get modestly more service, and those that pay nothing should have no expectations. Perhaps those persons who contribute to OSS or develop karma within OSS would receive a gratis memberships?