It's about 14 dollars per square foot, or a little more depending on where you get it. Greylite 31 is thinner, 1/8" I believe because it lets through 31% of light. It's not dark enough that you won't have to mask and paint the back or anything, it's just a nice arcade look over a TV/monitor. People love the 14 and I love the 31, just a matter of preference. I have a piece of smoked glass too and it's more grey than black, which it what makes the Greylite so nice. It's not a cheesy look at all.
GT