If you can find a silver Dual Shock 3 at Radio Shack it should ring up $24.99, so definitely try there for a deal cheaper than $30.
Either that or just buy one of those game/controller bundles. They're on clearance at Target IF you can find them. They typically have a greatest hits title and the controller in the same package, so it's like paying MSRP for the game and getting the controller for $30, since the package price is usually $60.