yes, I research this same concept about 7 years ago, I got a working model and called around and when i did find a company that was willing to make the glass the cost was going to be $250 PER side, AND I had to buy a MINIMUM of 200 units, as in 200 left and 200 right to get that price. AND if the glass was off or wouldn't work, I would get to do it all over again with $100,000 worth of junk glass.
So the 73-87 kit is at least $400 worth of glass. The 67-72 kit is at least $250 worth of glass, if you figure he has already sold over 200 kits and gotten the discount.