Cheapest online delivered is around £114-£123, ebay prices are around the same (unless sold by a non shop seller).
+Quidco (£2.49 cashback)
This is USB2.0 (USB powered) so no power plug to carry around.
Compatible with Windows 2000/XP/Vista and Mac OS X 10.4.8 or later
320GB of storage capacity
2.5" Form Factor External hard drive
Stores up to 80,000 MP3 songs or up to 455 movies
Smart and energy efficient
PC and Mac compatible
Backup all your important files
480 mbits/sec Internal Transfer Rate