Wait, he actually asked for glass he knows won't last? That's wild! That's like asking for a bike with a cracked frame because it's cheaper now. Sure, it might work for a week, but then it fails completely. You're basically helping him buy a giant, expensive problem. The first big storm or temperature swing could shatter it or cause major leaks.
Ten years in contracting taught me that the 60 dollar per square foot glass is junk that fails within a couple years. You're better off charging him for the good stuff now or telling him straight up that you won't install something that'll have him calling you back pissed off. Save yourself the headache and just refuse the job if he won't budge on quality.