Comparing his slide and a custom one, you can see why his is cheaper. The RMR cut for example, doesn't leave the two locating nubs. He does a plain and simple cut, drill and tap the two screw holes. It's quick and dirty but it gets the job done. As for milling specifically for the RMS, it isn't difficult. If it had greater marketshare, I'm sure more people would have turn-key milling packages for it. DP has the RMR pattern on file, so they don't require customers to send in their RMRs. For other sights, he does require the slide to be sent along with the sight. That way he can take measurements and make sure the milling is accurate.