[Son Of Skyline]

I was talking to J&L today about having a 90gal (48x18x24) drilled for an overflow. They kept mentioning that they'd replace whichever pane of glass that's being drilled with a thicker pane. So if I wanted a hole drilled in the back, they'd replace the whole back pane of glass with a thicker piece. Is this necessary if all I need is a single 1" hole drilled in the back upper corner of a 90gal tank? In theory, shouldn't it just cost like $20-$30 extra to buy a tank with a hole in the back, instead of the $100+ increase they quoted me? Thanks in advance.