Define a number of new topics created by a user

[dalbert]

As part of a subscription, I would like to allow users of a group to create up to 30 new topics in our buy sell forum, but have unlimited responses, and unlimited posts in other sections of the site (discussion boards).  What would be the best to implement this functionality (or is there an add on that would enable this)?

This quantity of allowed posts will need to vary depending on what group the user is in. 

 

Thanks