Buy back books based on amazon's api - Experienced Only

I need someone to build me a books buy back script based upon amazon's prices similar to cash4books.net. Customers will type in the ISBN of a book and a price will generate that shows how much I'm willing to pay. This price is based on amazon's lowest price (which often fluctuates). The price that I'm willing to pay for the book will be based on a set percentage of amazon's lowest current price. See example site, [login to view URL] Experienced dealing with amazon api and/or amazon related- script/database/software required.