Restrict a users node posting total dependent on a paid subscription role
In my opinion the best solution would be Ubercart for selling roles to users
 and Node Limit module to set a block on how many nodes can be created by certain roles (in a given period, optionally).

You should set up different roles, one for every different amount of nodes a user can create. Then with Ubercart you have configure a product for every role to be sold.

Then with Node Limit module you can configure the restrictions for every role.