opencart extension/module (price comparison like amazon)

Hi to all. We are currently searching for people who can create/mod an extension/module for opencart to do the following function for us. please see attached file for information. basically it is a price comparison. but it is only just an internal comparison. which mean it doesn't require any API that link to external store.(not sure is it the correct term). To put it simple, we will be enabling our members to sell their items in our website. However, they are only allow to sell items that is already exist in our database. If the items that they wanted to sell does not exist in our database, they will have to email to us and we will update our database as accordingly before they are able to sell it. so for members side, we also require you guys to help us to create a section whereby they are able to post the item(the item will be retrieve from our database and i believe it will be a whole chunk of list so i need you guys to help me think of a method to make it easier for the user to find it and choose,example make it to a list with scrollbar etc etc), price, contact etc. I understand that amazon links to other external source seller but what we need is only within our database. If my explaination isn't clear enough and you require some form of design for better idea, please get back to us.