I bought a couple of s/hand laptop hard drives for about £10 each, and a pair of (new) USB 2 cases for them, these were also about a tenner each.
I got them on Ebay. I've been using them for over a year now.
No problem making them up, just put the drive in the case and screw the top on.
There are usually plenty of laptop drives on Ebay as people fit larger ones in their laptop, then don't have a use for the old one.