Create price comparison website

I would need price comparison website, basically idea is that display item and in item page list sellers selling that same item and their prices and delivery terms. Technology choice is free. You can use ready made script, build from scratch or work you have created before. I have partnered with one company offering webshops as service and from their data I can import all items + merchants. So API would be needed to import that information. I have also partnered with one payment gateway that will maintain list of merchants and we can add one attribute for merchant id, so they will handle payments from customer to merchants, so this payment gateway integration is needed customers to actually buy products with in site. If you can provide mobile apps let me know that as well, I will then create separate project for those. Also if you have done prior work in these, submit links.