Paypal Integration into web builder

We have created a web builder that we would like to integrate a paypal payment solution into. We envision our clients loading a product description/info into our web builder (That we currently have) and have it auto generate a sales page for that product (We already have). What I would like to do is provide our clients with the ability to add their order info into our product setup form (Price per item, inventory count, tax, shipping etc. then put their paypal address in (Similar to Ebay) without having to go through all the steps of adding products to paypal. When our clients publish their page a client will be able to order a product and checkout using paypal. Our web builder will allow our clients to build multiple pages for multiple products so we will need to configure the software to be easy to use yet turnkey. The closes model I can think of is Ebay in terms of how this works,. Basically our clients are building landing pages to sell their products and we want to be able to offer them an easy method and way to merchant thier products. Basically as easy as adding their paypal ID and our system does everything else. I believe Pay Pal's API will do this (Automatically setup orders on the fly) but I have not worked with it in this manner. We are using a Joomla based platform but I dont know if that matters in this situation. (PHP, MYSQL). Let me know if you have any questions.