Automobile Auction SIte Like Ebay Motors

I need a automobile auction program to run similar to that of ebay Motors. I have lots of cars that I need to put onto the site to let local people bid on the cars, just like ebay motors. I have relationships with a bunch of car dealers and I'd like for them to be able to create a username and password where they'll be able to upload their inventory of cars to the web site. I also want for the individual user to have a storefront that showcases the cars they have, while at the same time, when they upload their inventory to their store, it also uploads to our main site. Here is a link to an ebay listing that I like...the user should be able to fill out a variety of fields that describes the vehicle: [login to view URL] How long would it take to develope something like this? Carl