User comes to main joomla site where he sees the description of the sites or local folder he can subscribe to. He buys the subcription and gains access to the needed content. When a user subscribes there are two options: to register him upon subscription or change his usergroups. And there are several subscription plans e.g. lifetime access, date to date, etc. If any access is finished the user can be just blocked and he will have to pay to prolong his access.