This has been brought up recently and I don't think there was ever a solution.
I know you could say, require a "$5 donation" for them to become a "gold member". Then just make only "gold members" able to create threads.
So you wouldn't be charging per thread, but for the ability to create threads for x amount of days.
--------------- Added [DATE]1241532505[/DATE] at [TIME]1241532505[/TIME] ---------------
Oh, and there are mods that limit how many threads a user in a specific usergroup can make (here's one i found real quick
https://vborg.vbsupport.ru/showthrea...=limit+thread*)
So maybe you could combine that with the idea I posted above... who knows...