One of the studs on my brakes is bad. If I take this to get a brake job how much would a mechanic charge to replace the stud? Just a few dollars or quite a bit more??

Or you taking about the wheel studs, or caliper bolts? Neither should cost much the wheel stud is easy to knock out with a hammer and then put a new one in. you can pull it in with the lug wrench when you get it started. The caliper bolt is not a problem if the threads are O.K. in the bracket.