You can charge for posting on a certain category from the add/edit page. For example, on the demo, on the Classifieds category "Cars", you could set the post cost at https://www.ultimatewb.com/demo/admin/edit_page.php?id=77 (scroll down the page for the field).
You can charge for access to certain sections of your website by charging subscription fees for membership in a group, and restrict access to those web section to that group. Here are the related user manual topics on this:
"How to Restrict Access to Members, or certain Members/Groups"
"Item Payment Processing: Downloads Access/Add Member to Group"