Cash for scrap gold

Hi there I am looking to build a website similiar to the cash for gold websites that are popping up everywhere. I need an area where customers could calculate the gold,silver and platimum value by the presentage spot price that will be pre determined by me. I need a registration section for basic info,area where customers could track their parcel from the post office, and links to facebook ,twitter [login to view URL] advice as this should be a straightfoward project.