Backend UI with Active Directory like features

Hi, I am looking for someone to develop a back end user interface for my customers. This user interface is for paying customers only with a prerequisite that the customer at least purchase a basic product for the free version. The backend needs to be subscription managed. In other words the customer should only have access to certain items if they have paid for them and restricted if they have not. All of my products will be information based and in a video (flash) or pdf format. I am unsure of the costs associated with developing such a requirement. Please let me know your thoughts if bidding. Regards, Andrew