Please don't hold your gunsmith to this, but I would say $25-30 for a normal crowning, no complications. A new barrel will cost over $100.
I would tend to agree with this estimate. If your barrel is the old barrel bushing style, it's a simple matter of chucking it up in a lathe and carefully polishing (or cutting) away the nicks. If the nicks are not that bad, it will be pretty much a simple chamfer job.
If you have the later muzzle end integral barrel lug it is a little more difficult to chuck up in the lathe, so it might
tend to be a little bit more.
At any rate, crowning is not going to be in the "hundreds of dollars' category unless your local gunsmith is "on drugs."