There is no area in wpForo, there are forums in wpForo. And you can set different Forum Accesses to different Usergroups. Each forum can be available for certain Usergroup. There are meany examples explained how to manage Users accesses in Forums:
Once you understand Forum Access management ways you should install and configure some Paid Membership plugin for handling members payment and levels. Just let us know what Paid Membership plugin you're going to use and integrate with wpForo.
In case you want to say thank you !)
We'd really appreciate and be thankful if you leave a good review on plugin page. This is the best way to say thank you to this project and support team.