TSK here im selling over 3 double chests filled with glass!
5 diamonds for 2 stacks buy now before it's gone!

thats too expensive
maybe if it was 1 diamond for 1 stack

Yep, very expensive. You get a diamond every 2 minutes about branch mining. I could gather several stacks of sand in those 2 minutes, and smelting them into glass is a negligible cost.