Database driven shopping cart site

I need a website created with a shopping cart. I'd like it to be database driven so that I can update information to the database as needed, and the shopping cart site will reflect the changes. Pick your own database, (I'd prefer a free one) but I'd prefer that it be built for Windows, as my website provider will most likely be hosting me on a Windows machine. Ideally, there should be a shopping cart site that can be replicated to three separate sub-domains, each with its own inventory and images (can be built to simply use three distinct database files if needed.) I'd like to have the site running soon after we select a bidder. The site will be running at least 20 items for sale at any given time and potentially as many as 300... if this impacts your bid, please let me know. Ideally, I'd like to be able to list a product for sale while keeping track of my inventory on that product, eliminating over-sales.