He normally charges $125-175 per 2" marble.
Forget the shift knobs- get in on that!!!! But seriously, there are
people who will spend a hundred or more on a knob (burl wood, carbon fiber, titanium, etc.), but whether the hand made glass knobs are among them, who can say w/o trial marketing them? I wouldn't invest anything close to $2000. If you want to see if there's a market, make up two or three and see if they sell on eBay, and if they do, for what price.
I think lighting them from inside would look real good...