I wouldn't for that large of tank. I've heard of ppl use it for small tanks. 20gals or less. I don't think that plexi is stiff enough to hold that much weight. But I could be wrong.
i found some 4x8 sheets of cell cast by me that are 1in for 716 each i know you get a deal if you buy 3 or more, but i don't know how much the 1.25in is.