There you go bro... do a pay per post... LOL... seriously... charge like a penney a post, and at the end of each month charge the users CC for the posts... Also, posts that have attachments could cost like $.1 or something.
ie... a user posts 400 times in a month, they pay what $4 for that month... And if the user posted 10 attachments they would pay an additional $1. This way users who do not post much will pay less, as they did not contribute as much to the site load.
of course, less posting users would still have the bennefit of all the good dialog and information on the site... so I'm not sure what the benefit of posting for some people would be...
And would be much more complex and require more admin work... so... maybe not a good idea after all... sorry, but just brainstorming to try and come up with a way to help... Whatever eveyone decides... I'm in...