c# + Ajax Customized Shopping Cart

I need a very custom "add to cart" process that requires some interaction with a SQL database. Must be ajax but degrade gracefully to a server side version if Javascript is not enabled. Must be cross browser compatible. Involves both Backend for adding products and front-end. Product price will vary. Product attributes price will change based on location selection. Must design a very elegant class structure in c# ASP.NET and integrate with an existing system. This is only a modular design and not a full website design. No open source carts allowed. It is a custom design. Must have very excellent User Interface design skills.