Pricing can be tricky, especially once the emotions factor into any purchase.

And when it comes to an SRT-6, the emotions usually run pretty high.

For a reference point, I bought my (Used) 2007 Roadster from a Chysler Dealer, it had 12K on the odometer, very, very clean interior and exterior, and it had the right color for me (SSB/Cedar), and I paid $18.5K. (And I did get a 90 day bumper-to-bumber from the Dealer).

Going with a private seller, you should have a some play on the price, but to be honest, a 2005 SRT-6, with 20K, and lets assume it's really clean, if you can chop some off of the asking price, it should be a good deal.

If you plan on keeping the car for a while, and you will enjoy the juice of the SRT-6, in the big scheme of things, getting a very big discount off of the current asking price may amount to a hill of beans in the long run.

Again pricing is very subjective, but if you both walk away from a deal feeling quite satisfied, then you can't ask for better than that...