[Vaupell]

Well the subscription feature can also place users in a different usergroup.
and the thing about allowing sertain permissions is something you set,
nothing is set from vb by default.

"basicly" what your descripeing is excaktly what vb default subscription does.
but you just have to set it up yourself,

start with creating a usergroup, then look through the subscription options
when set, create payment methods etc..
then finally advertise subscriptions..

Alternatly you can use one of the many donation modifications where
someof them allows you to move user to another group when donated..