Add PayPal Automatic billing to custom PHP (code ignitor) shopping cart

[login to view URL] is a PHP website selling silver coin subscriptions. The owners of the site want to change from the Paypal subscription service to the paypal AutoBilling. Currently as the price of silver coins changes frequently, the owners must cancel subscriptions and have the customer "re-signup" to continue with the service. This is undesirable. Paypal's Autobilling service allows customers to choose a maximum amount they are willing to pay for a subscription so that as the price of silver increases, the owners of the site can increase the monthly amount of the subscription up to the maximum the client is willing to pay without forcing the client to re-subscribe every time the subscription price changes. The website is built with PHP Code Ignitor. PHP developer must know this framework and be able to quickly remove the old subscription service and add the autobilling feature so signups are properly recorded in the MySQL database, affiliate commissions are still tracked and monthly Paypal notifications of customer billings are still recorded accurately. A field will need to be added to the admin page so that an admin can change the minimum autobilling price. If the price is over the customer's limit, paypal sends a notification to a page on [login to view URL]'s site. Account should be suspended and an alert email sent to the customer. You will code directly on the website and be given temporary FTP account access. (Site is live but not currently being promoted) Changes must be uploaded and tested immediately.