If you are using paypal standsr, look at payloadz.com. They specialize in this.
If you want to build your own you will probably need a database and Digital File Pro.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.