Dental offices all over the country have scanners that use regular cameras + photogrammetry to create 3d models of your teeth. They've become pretty widespread with the rise of Invisalign, Smile Direct, and others. These scans can be pretty inexpensive, like a few hundred dollars or less.

That depends if the 3D intraoral scan can be done by running an app and then putting your (open) mouth over the rear camera with the LED on, and moving it around until it beeps. Or if you have to go into a doctor's office to get it.

The custom design is simply a matter of business process on top of a standardized scan.

Could be, but I would imagine if they were able to certify this as a medical device that it could be covered in part or in whole by insurance in some (non-US I would imagine) countries.

This does not need to be expensive. I expect the price to drop down with economy of scale