http://www.myg37.com...ger-system.html
Been following this for a while, above is the thread on myg37.com about the work that they have been doing on it.
I priced up their Stage 1 single SC kit and after you add local installation and tuning, auto trannie work (if required) and launch control (to make it useable) I wasn't going to get much change from $15,000. So I would imagine that something in the $18,000 - $20,000 ballpark wouldn't be unreasonable.
Of course, if you had a lift and could do the install yourself you would save a BIG chunk of that. It would potentially be cheaper to ship the car to GTM, have them do the work and ship it back, as their labour rates and install/tuning time would be significantly less. This would guarantee that it was installed and tuned correctly as well.