It would be outrageously expensive if he needed that keyway cut with a broach, which is a long drawbar with about three dozen cutting teeth, used for cutting keyways on the ID of bores.
Most machine shops don't spend the money to stock all the different sizes of drawbars or buy the machine, because it isn't multi-purpose.
Fortunately, he could have the keyway cut by a shop that has a horizontal milling machine fitted with a standard mill vise...the cost should be about $75 if he can find a shop nearby willing to do it.
I just wanted to clarify the difference between the two procedures because if he calls around to several machine shops asking if they can 'broach' a keyway, he'll get a much higher quote, if they have the machine to do it at all.