The last time I called a locksmith they told me it would be 100 dollars over the phone. When he came out he told me it would be 400. It wasn't even a deadbolt just a regular front door.
Oh ouch :( Then I guess your only recourse would be to tell him you'd only pay him the $100 you agreed upon, although I'm sure that wouldn't work if he told you about the increased cost before he unlocked the door.
I'm still mad about that.