The Roush 427R was a modification of the Ford Mustang that has been equalled or surpassed in raw engine performance by many newer production Mustang models as of 2015. It is likely that a used Roush 427R is more expensive and less reliable than these newer models.
Produced from 2006 to 2010, the Roush 427R was so named as the modifications to the base Mustang engine boosted its output to 427 horsepower. These included a Roush supercharger and ECM calibration. As these are aftermarket modifications, there is a higher chance of mechanical issues with a Roush 427R as compared to a factory Mustang. In addition, prices for the Roush 427R have remained relatively high due to the rarity of the vehicle, with prices in the mid-$30,000 range common as of March 2015.
In comparison, a new 2015 Ford Mustang GT has a base MSRP of $32,300 and produces 435 peak horsepower from a naturally-aspirated engine. It is less expensive and more likely to be reliable than a used Roush 427R while producing slightly more power. In addition, a new Mustang is covered by a factory warranty from Ford, while a used Roush 427R is unlikely to be covered by a warranty.