Do It Yourself Website Builder

I want to provide a shopping cart system where my clients can design their own websites/storefronts (drag and drop) by uploading their own graphics (or choosing from selected ones available) as well as maintaining (individual admin cpanels) the site/stores themselves. I would need assistance with installing the script/program. I am working on a low budget as this is for a smaller market of online businesses. If needed I can provide some sites that could be used as clones. However, I would like my own script designed if possible. Some references or portfolios would be appreciated. I need a custom database/shopping cart built (a Do It Yourself Website Builder) with the following capabilities: Several Layouts to choose from. meta tags/keywords capability for every page or product. Splash Page (welcome page) Unlimited Categories w/Unlimited Products Unlimited Sub-Categories Order Information Page Links Page Contact Us Page About Us Page Picture Pages (display product choices, color samples, etc.) Unlimited Extra Pages (contest, newsletter, recipes, project pages, etc.) Order History & Customer Listing Built In Shopping Cart: I need the DIY to maintain it's own database driven shopping cart with these optional features: Automatic Shipping calculator ~ Connect to USPS or UPS and get real time shipping rates. Or use your own shipping calculations. State Sales Tax calculator. Accept Checks, Money Orders, Paypal or Credit Cards through one of or a built in merchant Built in Coupons and Discount Codes. Automatic Inventory Control: the option of controlling the inventory on a product by using a checkbox on your product form. ie. one of a kind items. Other suggestions to make this even better are appreciated!