I think you’d have a tough time spending 3 million to build a single guitar in an existing shop.
The perceived value of a one-off Martin is due mostly to the fact that Martin has been around since 1833 under the same family doing the same sort of work for its entire history. And for a relatively brief period of time (the perfectly timed post WWII era when baby boomers discovered acoustic music and began to run the market for its paraphernalia) they were the best acoustic guitars available.
Hard to duplicate that in a new instrument. I’ll bet my SCGC sounds as good as or better than this $3millon museum piece.