You don't need one, but you are better off with your own buyers agent. The major listing brokers for bank owned properties have hundreds of properties on their books. Of course, they'll do their best, but if they are swamped with dozens or hundreds of calls and emails it is only natural that you'll have to wait your turn. There will be no differnce in the cost.
In the current market here in Central Florida the listed price has virtually become the floor at which the bidding begins. If you are not in with a solid bid the first few days a property is on the market you've got very little chance of getting it. Another reason to work with a buyers agent who can notify you daily on what's new to the market.
Good luck with your search,
Weichert, Realtors - Hallmark Properties