Marketplace forum mod

[patsfans]

I was trying to find something that would allow me to create a"Marketplace" forum where I would charge annually for a user to be placed in a usergroup (ie: Forum Merchant) with ulimited posting access. The Forum Merchant status would allow one to create threads in the Marketplace forum. Here they would advertise their wares, events, post links and photos, etc. Only Merchants would be allowed to create threads, but everyone could look at them but wouldn't be able to reply. This part is easy, and I know how I could do it since I already have a "premium" forum on the site and people currently pay for access to that one.

But here's what I really need and would like to integrate it into the above mentioned forum: I'd like to have the option for a user to purchase one-time merchant status for the ability to create one thread topic in the Marketplace forum. This way people who aren't really doing this full-time would also be able to create just one listing to try and sell a single item. So this would be more of a pay-per-post (ie: they'd have to pay for a single post) option that I haven't found a mod for yet.

So if anyone have any suggestions (or if this inspires a mod ) please let me know.