Direct school to school auction site

We have developed a network of public and private schools that are interested in selling their used or excess inventory directly to other schools rather than through a middle-man company. We now need to build the interactive website to handle the transactions. A customer should be able to list, upload photos, and provide descriptions of their items for sale. A customer should be able to search for products by category as well as by a keyword search. We want the customer to be able to list the product for sale or for auction, much the same way eBay uses the auction or "buy now" option. In fact, the website should operate much the same as eBay or Amazon does. The website should also process payment and transaction fees to be paid to our company. At it's maturity we expect the customer base to be roughly 100,000 organized schools as well as many more individual users. We desire to develop a user list as well. In order for a user to participate they will need to provide personal information at sign up.