CNET has a section on its website that contains online stores that sell the Samsung Galaxy S4. In addition to price, if the store has any promotions for the phone, then they are listed; for example, T-Mobile has a no money down offer, as of April 2015. The tax and stock status are also shown as well as shipping costs, if applicable.
Best Buy is selling the phone for just over $700 total, including taxes. On the opposite end of the pricing spectrum, Wal-Mart is selling it for about $430 and T-Mobile is selling it for just over $400, according to April 2015 pricing information from CNET.