Having a mill, lathe and an excellent understanding of firearms being that we are gunsmiths, we can reproduce one off parts for guns that no longer have parts available for purchase.
When we do these one off parts we charge a baseline of $100 which includes one hour of shop time and any additional time is charged at our normal $70 per hour. The reason we do this method of billing is that we may need to make special jigs to hold and work on the piece. As a result it can take more time to make the jig than machining the part itself. At the end of the day it comes down to the order of machining operations and sometimes having specialty taps or dies manufactured.