How much to have someone drywall a garage?

I'm was thinking of having my parents garage drywalled. It is a 30+ year old house with the original dry wall (no finish) so it's in really bad shape. It probably just needs to completely come out and put new drywall in. It's 21x23 sq ft, including ceiling..ceiling height 9 ft. Anyone have experience with drywall and know a ballpark range of what it would cost?