Custom Shopping Cart Modification

We need a special modification to our existing shiopping cart and CMS. We want to be able to set two (2) prices for each product. (A List Price, and A Lowest Acceptable Price) When the customer enters the site, they will see the list price, and be allowed to enter their "Best Offer" The price they enter will be compared to the database, and the page result should most likely use Ajax, rather than re-loading the page. If their prices is within the range allowed (between the List Price, and the Lowest Acceptable) then their bid will be accepted, and they will be allowed to check out. For an example of how the site should work visit [login to view URL] (this is a competitor's site for comparison) Additional Information: Our C.M.S. is custom scripting, open-source, and NOT based on any framework. We will need integration into First Data's Payment Gateway. ([login to view URL]) We offer LIVE CHAT SUPPORT during the project (Only After a Provider has been selected) All work to be done on our server.