I'd be inclined to stick with the glass build for that size, unless you really want the extra height for something specific. 12mm glass will be fine for a 2' high tank (in fact you could stretch it to 26" tall and still keep the safety factor close to 3 with 12mm) so the glass build shouldn't be too expensive and you'll end up with a better looking and more durable tank. If you were set on the 3' height then the ply would be a cheaper option for sure as you'd be looking at more like 19mm glass, which would be very expensive.