Computer Hardware Database/Cart

My client is wanting more of a database driven website with a back end section that will allow them to add and edit the product data themselves. Similar to a shopping cart. My client gave me this website as what they are looking for in functionality. [login to view URL] They will be selling the same type of products as this company and should function just like this site – Only I will be designing a new look for their company and providing those graphics for you. At first glance it looks pretty simple with the categories on the left and products listed in the center. But if you were to click on one of the products on the right panel from the home page under workgroup servers (Sun Netra 1280) you will be brought to a page that lists that server – but also all the products that belong to that particular server. They want to list a used price and a new price. Instead of a buy it now or add to cart button they want it to say call us and it go to a contact page. Later down the road in a year or two they will want to add shopping cart functionality to this site without having to rebuild the whole site. I would like estimates for this on a project basis rather than an hourly rate. I am not locked into php or linux but is preferred as I already have a dedicated server.