Is your main purpose to back up your operating system or main files or for storage of files?
Cheapest route would just to use some free software to do your backing up to another drive.
If you want something that will hold a lot of drives, this thing is excellent:
http://www.memoryexpress.com/Product...23479(ME).aspx
If one-touch backup is so important that the Free Agent Desk/Acer Aspire things are probably better.