As holdover said, there are many variables. When I built my 28x34 a couple of years ago, I had 12k in the concrete work alone. That was the only part I couldnt do myself. But I needed a fair amt of excavation done and lots of fill to level the area (rear needed about 3 feet worth of fill to bring it up to level)
After the concrete, the materials for the rest of the garage add up quickly. The ocst of them will depend several things, including, but not limited to whether you are going to have power (and how much), if you are going to finish the inside (drywall, metal roofing material, etc), lighting, heat/AC, Siding type, etc.
