Welcome to the world of Xbox 360 controller collecting. Just a heads up, the more rare controllers will sell for more than $30 even in terrible shape.
Have you tried checking eBay for the controllers you are missing? I am currently missing that Radioactive/Gamestop exclusive controller and it is a pain to find.
This one looks in decent shape on the front:
http://www.ebay.com/itm/371274679513