How much would it cost to build an e-commerce website like Ebay?
Ebay is an application that allows every user to signup, provide shipping info, and buy everything they need. If needed, a user can also start selling their own items as well - he just needs to make a couple of photos, set description and price, and he is ready to go!
To help users find products faster, eBay also provides a sophisticated filter and sorting mechanisms, allows a user to add items to a watch list, and so on.
If you would like to create an app similar to eBay - let's figure out how much time it can take, and all the cost to run a website like eBay. If you don't need some of the features - just check those items off, and it will update the estimation.