Subscription script required for Oscommerce site

We have several Live Oscommerce B2B sites.? All products/catalog are visible.? But prices and buy now buttons are replaced with Log-in/Register. We currently charge a monthly subscription/membership fee via paypal to view prices & enable purchasing.? Currently we have no way of blocking “expired?? memberships. We need a more robust system.? We thought of doing something along the lines of: 1.? The visitor selects a membership level (1 month, 6 month, 1yr etc) by clicking on a paypal link on our website.? 2.? A date field could be added to the customer table (which is visible in admin) and depending on which membership level is selected, a "block access" date field is written to that customer (which would be 1 month, 6 months or 1yr forward dated).? 3.? If the customer tried to log-in after the expired date, a message could be displayed "your membership has expired, pls renew etc etc). 4. The only thing I haven’t figured out is how to handle customers who have already renewed before the expiry date. ? I understand Paypal IPN can send data back to Oscommerce.? Maybe the new “expiry?? date could be written to the customer record when they have renewed their subscription.? Otherwise access to login could be blocked until user renews membership. Any other suggestions will be greatly welcomed.? All other issues can be discussed via email/MSN If you think you can help, please contact us with details of any sites you have worked on.? If you have a readly made solution to this it would be nice to see a working demo. Hope to do business with you in the near future.