If it is a V8 Roush, that is a darn good deal IF everything is top notch with it. The Stage 2's (the first V8 package) comes with a pretty nice suspension upgrade package like the Saleen S281's get. It makes a BIG difference in handling, plus it already comes with a nice body kit and wheels. Make sure it is a genuine Roush though. Ask to see paper work, make sure it has all the identification plates and labels etc and get a production number. You can then call Roush with the VIN number and they can verify if it was indeed "Roushed".
Really, anything less than 20k is a good deal for a new edge Roush. (Stage 2 and 3).