Bestbuyuniforms.com
Just search for "coveralls" when you get there. I got the Coveralls - 65/35% Poly/Cotton Heavyweight in White, but they have them in Navy, Spruce Green, Postman Blue, and Shell Brown too. They also have a set of Bright Orange ones for $19.95 that I could totally see someone using as a Rebel pilot or Bossk.
I have been looking for decently priced coveralls for almost a year now and this is the best that I have found.