We've put in a shopping cart for a client that's not working, and we need some help!

The cart is currently using the WP-ecommerce plugin. Even the developers of this plugin admit this thing needs to be scrapped and rebuilt from scratch. Yeah. Anyway, the products on the site require a very sophisticated level of functionality that affects shipping based on country and zip code.

We've hacked the plugin to pieces to make this work, and there are still errors that are costing her sales. It would be easy to limit shipping on a product-by-product basis, but that's not the way her store works. Like on Cafe Press: I want the slogan that says "My mom can beat up your dad." Once I select the slogan, I can choose to purchase that slogan on a t-shirt, mug, or bumper sticker. However, if I live in London, I shouldn't even be offered the bumper sticker, for example, since it can't be shipped.

See our problem? Got any WordPress solutions for us??