You could do it with Prestashop with a specific module...Find a programmer or adapt an exiting module...there great place as DP or Elance where you could find someone who help you to develop a specific solution...
I would strongly recommend looking at Prestashop. My experience with the general usability and the support provided for a free platform is second to none.
Also kind of looking for the same thing, hope I get this thing through this thread!! Comparison shopping
Check out Opencart, it's free as well. A lot of people are hot for magento, but since they stripped out a lot of core features from the community version, I have been seeking alternatives to recommend to clients.