Aren't you jumping the gun? So far the repair man hasn't given you a bill, and he hasn't failed to fix the machine since he's waiting for the arrival of a part. I don't think a month is unusual since shops often have a backlog and don't put the newer machines on the bench until they're finished with the ones already there. So, although you've been without the machine for a month, he probably hasn't been working on it that long. He probably wants to ship the machine himself if that becomes necessary because he can be sure it's properly packed. Mailing places do not necessarily know how to pack sewing machines.
Did you receive any paperwork when you dropped off the machine? I would expect that it would include an estimated repair bill, or that the shop would call you with an estimate after determining what's wrong with the machine.