Its probably going to cost you about $15,000 to 20,000 thousand. This all depends on how big you want it, electricity, heat, concrete floor, second floor, shelving, permits. The City inspector will want to see your plans.
$25,000 should get you a basic two car garage, but the price can be much higher depending on the materials that you use. If you use meatal roofing that is going to cost more then shingles. It will also depend on how many rows of block you use in the foundation.