Noah Schwartz, a machinist who used to work for Marty Forscher in New York (Professional Camera Repair--the best shop in the business for many years), posted on photo.net a while back that a properly machined lensboard hole should also have a recess for the retaining ring, and I think he incorporates some relief on the front for the levers on the back of the shutter, so it's not always just a hole. Here are some of his lensboards--
http://photo.net/photodb/folder?folder_id=569861
I don't own any of these myself, and the diamondplate seems like a bit of a gimmick, but they do look to be very well made, and checking completed auctions on eBay, he sells recessed Sinar boards with a Copal 0 hole made this way for $60.
When Steve Grimes was alive, drilling a lensboard was $15-25, plus a bit more for mounting a flange if necessary.