They run that stuff, I dont know the prices. There is a contact button on that site, ask them and they should be able to help you out. We let them handle the advertising stuff

and to be sure we are on the same page, being a paying vendor still means you need to keep your threads inside your shop forum, you just get to put a banner in your sig and banners across the top of the page

Most shops find it acceptable to put their link to their forum in their sig.