It's not just a supercharger on the SRT-6 that separates it from the standard Crossfire. The engine in the SRT has been completely reworked. If you source out all the parts and buy them used/refurbished rather than new, you can install the blower alone (no engine upgrades) for roughly $1500. I've been looking for parts for some time now. There were a couple AMG blowers on ebay selling for around $250, but I was never able to win an auction for one.

In addition to the blower, you'll need some other parts - two AMG intake manifolds (not cheap), the intercooler, coolant lines, new engine cover, and I think there's an adapter for the throttle body as well.