The SRT-8 is definitely fast, especially for an SUV. But like the other cars that use the 6.1L V8 engine (Challenger/Charger/300C), it loves gas, and even more so since it's heavier than the cars. New, they can be very expensive, but if you look for a used one, they are super cheap... thanks to Chrysler's inability to hold any value whatsoever.
Check out the link below, the first one is an '06 with 30k and is only $25k. Now if that is not cheap for that kind of performance and cargo capacity, tell me what is!