You mean an external hard drive that connects threw a USB? I'm pretty sure I saw one that was 1TB at staples.
No, I mean a special cord that will connect any regular internal hard drive to a USB connection, instead of to the IDE or SATA connection inside your computer. It eliminates the need for buying drive enclosures, or buying normal external drives.
That one is listed as $50 on memoryexpress.com, but I'm pretty sure you can get those as cheap as $20 if you look hard enough.