Just an fyi, I believe 1/2" glass is more rigid than 1/2" acrylic. True, acrylic is pound for pound stronger than glass, but all things being equal, acrylic will bow out under water pressure...hence, a tank built with 1/2" glass vs. an acrylic tank of the same dimension, the acrylic will be built with 5/8"-to combat bowing. Just a thought. ..and I may be over thinking things. It's just been my experience....
Glass is very expensive...especially custom ordered...and 8x2 is custom because they have to cut it...long ways...
I have had good luck with glass that is repurposed...just for fun and curiosity, ask around to some door and window places and see if they have any Hurculite doors laying around or glass that was ordered for a project that fell through. I got a 3'x10'x3/4" $5000 piece of glass for free once. It was a big glass door from a building lobby the door company took down for a tenant improvement project for a high rise in L.A.
They were going to throw it away. I also got four pieces of 4x3x1/2" tempered safty glass for free....
I don't know what your plywood dimensions will be, but to avoid spending almost equal amounts in construction material costs, shop/ask around a little...ypu may be pleasantly surprised what people and businesses throw out.