I need a price comparison website

I need a price comparison website built which will be launched for September so website need's to be finished before end of August. Website will be free to use and is for a niche market, IP system will be in place and website need's to have function's to allow client's to log into their own accounts to change/admend details and make payment's I will need access to the admin area of website to allow me to suspend account's, make changes and amedments. I will need a cms systems with unlimited pages so as business grows I can add new pages.Website need's to be simple,easy to use and understand.