users must pay for a period of access to certain sections

Hi,

I need to build a site where architects and lawayers have articles about building for people who build ... they want that the users need to pay ... ie

1 month usage = 60$
2 month usage = 40$

is there a module that does this and that sets the user role back to a lower level when the subscription period has ended? i haven't quite found something like this?

thanks