It will be much cheaper to buy computer case fans, cut the wires and wire them up to a 12v DC adapter. You can get the 12v DC adapter at a local Radio Shack, or probably cheaper online. Each computer fan you get will have a milliamp rating, as should the DC adapter. Just make sure your adapter puts out enough milliamps for the fans. You can wire up more than one fan to a single DC adapter, provided it has enough juice. I think DC adapters will commonly have between 800-1200 milliamps, while the fans will probably draw between 100-200 milliamps.