I used tempered glass in one A about 20 years ago.My friend that does glass work said that he'd hooked up with a new tempering outfit,and it wouldn't be much more to temper it.He cut the plate,ground and polished the edges,and sent it out for tempering.It was his one and only transaction with that outfit.It was astronomical.I get it being pricey,as it's a multi step process,as tempered can't be cut.( not feasibly for a small glass company anyway)Plate glass is cut,then boxed up,and sent out for the tempering,and has to be brought back.Billing four times the estimate was not the way to go.