I have been looking into these carports that you put up yourself and can be enclosed. A 20X25 with a 7.5' wall height enclosed would be less than $3000. You are responsible for the garage door though. It will have the opening. We have a local dealer. You can check out the site below and see if there is a dealer in your area.
http://www.versatube.com/
Gus
http://www.versatube.com/
Gus