A few years ago I was building cabinets to make some money. When I needed to make glass insert doors I always just had the glass shop I used cut the pieces to size, and send them out for tempering. Some of these were 4 foot x 1 foot pieces of opaque patterned glass, and the cost per piece wasn't outrageous. I could never tell by looking if they were tempered or not, so the corners didn't round over or anything like that. For relatively small tanks, like 3 foot long or less, this might be a good way to go. The only problem I had was the inaccuracy of the cutting the glass place did. That could be a real problem for a rimless tank.