I bought one of these
http://www.aitrend.com/HD-307A.html
and added a maxtor drive to it.
I generally use it as a firewire drive though it works fine as a USB drive.
I also have one of these but it is over your price point
http://www.amazon.co.uk/Buffalo-Link.../dp/B0007R6CF8
This is on 24/7, though the fan is getting noisey. Bought a new fan - need to get a soldering iron - transplant planned for next week.
Microsoft Sync Toy is good for moving stuff back and forth between drives and getting backups of music etc.