My client required a question and answer component with following flow.

1. Admin can create a category for questions
2. Admin can create many number of questions and answers for a
 category.
3. Admin can set up payment integration to view the answer for a
 category. i.e to view all answers for a category then the user have
 to pay in our web site
4. In front end the user subscribed for a category then he can view all
 answers in the category.
5. If he want to view one more category answer then he needs to pay in
 our web site.

I am open for any paid version in Joomla or Wordpress in above functionality.

Thanks.