add subscription facility to CRE B2B 6.4

We are looking for someone who can modify CRE Loaded B2B version 6.4.1 to do the following: Allow customers to pay for a time limited subscription (say one year)that permits access to the whole site giving full access to all downloadable products available on the site. At the same time we want individual users to be able to download individual files and be charged a individual price. I assumed the FDS would allow that but I have failed to work out how to do it.