Not sure if it would work for you, but I've been using a simple cart called VP-ASP 6.5 (Shopping Cart Software – Ecommerce Solutions and Web Hosting From VP-ASP) for a couple of years. Whole thing is written in ASP and source code is fully exposed, so you can customize all you want if you know HTML/CSS/ASP. Quite inexpensive too, ranging from $99 to $499 depending on options.

It's not without limitations, but works fairly well for our purposes. I would be curious to know other best in class shopping cart options. Any good roundups/review sites?

Thanks,

Alex