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 rate of $100 per hour with a one hour minimum. 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 well as the additional skill set that is needed to run the equipment. 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.