That's closer than I thought, although apple like to charge the earth for a 1/2TB drive!
I'd still need a drive to get the CD on it though and find external drives cheaper per bit.
Although Apple manufacture a separate USB drive for �65, I prefer the Firewire/USB drive from LaCie for �85 (or their Firewire/USB Bluray drive for �350).
Yes, Apple mass storage devices are pricey - and although I would buy a six-bay ReadyNAS Pioneer, Apple do sell the 'Promise SmartStor DS4600' complete with 4x1Tb drives for �699.