For some reason I used to find expensive thick beveled glass table tops by the garbage, out by the street, etc. I've found about 5 of different shapes and thicknesses and they would be great for the front of the kind of tank you're thinking of. I haven't seen any in a while though.

Google "garf's 140 gallon reef tank construction". This guy makes tanks for relatively little money and gives the directions. All but the front is plywood.