As photographers shoot more and more images, they require a more and more hard drives to hold all those images. The cost of an external drive is a combination of the raw drive and the enclosure/power supply. WiebeTech makes a power supply/firewire interface that does not include an enclosure and allows you to quickly connect raw drives and quickly swap them out so you can buy a stack of inexpensive raw drives and then switch them out as you need to use them.