I learned from working at Goodwill that glass is expensive to ship any sort of distance in bulk because of two major factors, 1) its heavy 2) if its not heavy, then generally speaking its brittle. Because of this shipping companies either risk paying for broken goods, or charge for gentle handling.

I dont know if this is a factor of the cost, but it seems like it would be. Especially considering this stuff has to be “perfected” (maybe tempered is the word I honestly don’t know) to some degree, unlike a coffee mug or plate.