You can sometimes get the Rustoleum epoxy stuff real cheap. I had my garage done a few years ago. Prep work is key. The only issues I've had are a bleach container leaking that I didn't notice right away. It ate through the epoxy. Also along the edge I've had a piece of concrete chip, but that's really more a problem with the floor and not the coating. It's hard to beat for ~$100 to do a 2 car garage, but it sounds like you may have a lot of prep work to do it right.