I took a key in to be copied. Little Jim did the work for $3. However, he pointed out that the cuts on the key weren't very deep. He said a burglar using a special key could easily manipulate the tumblers and defeat the lock.
At his suggestion, I removed the lock from the door and brought it to him. He hoped to re-key it, but the cylinder was old and shot. So he dug out a used cylinder from his collection and re-keyed that. Cost: $10, including two new keys. He did the work while I waited.
Little Jim is very pleasant, and he knows his business. You won't do any better!