Question: I am a sole developer currently backing up my source code to .zip files on an external drive. Is it worthwhile for me to start looking at code repositories? What's the simplest, cheapest option for me? (ie. There is no need for lots of fancy features as the repository is just as a backup and not for sharing with a team).

... Forgot to mention. I use Visual Studio 2010 only.

Answer: 
Anything would be better then zip files.

For personal projects I would start with Git or SVN. Both are free and have addons for VS.
SVN would be perfect for you!!

I use Visual Studio 2010 as well, and there's a great open source plugin for working with SVN - [AnkhSVN](http://ankhsvn.open.collab.net/)