I have a 6" ss model, I love it. That one you have found for 500 used wouldn't be too bad of a deal as long as it is in like new condition. Also the new ones come with the Houge Monogrip which I prefer to the older GP100 grip with the wood in the center. I got mine for less than 600 new I don't remember the exact price but that was a year ago.
Vote Scott Walker for Governor June 5th 2012