some tech guy that works for my parents knows this site that sells super super cheap stuff (i think its refurbed but w/e) so ill find out tomoro and let you know. I know the site is legit because i think we have bought some externals from them before. Ill tell you what the site is tomoro because i cant remember what it is off the top of my head.
if you have a store near you they always have super low prices and a lot of good stuff. external hd's are super inexpensive now, so just get like half a terabyte or something and youll e set.
Dont buy a regular external, buy an external enclosure they range from 20-40 bucks, then go buy the biggest hard drive you can find. regular hard drives are cheaper than externals, this way you can go buy a hd or 2 and just pop it in the enclosure.