how much do you make per hour? a competent transmission repair can do a bench rebuild in a couple of hours, 3hrs tops. to remove and replace the trans should take 4hrs. It probably costs less than $300 in parts, unless it's major broken. So do the math. If he is making twice what your making per hour, I say do the work yourself. If it turns out ok, and you like the work, you just gave yourself another skill, and possibly a side job.