I think there is some pricing on the site. Seems like the THX version is about $32 per sheet, which is 4'x8' I guess. There is a lot of information with relative reduction available on that site. I'd spend some time there and look at all of the installation sheets and data sheets. I gave you the home page, but here is the QuietRock THX page:
http://www.quietsolution.com/html/quietrock_thx.html