Seems like a good price compared to what comparable cars are being priced at. The key is how tight the drive train is...especially the transmission. Tremec 3650's can be all over the map in build quality...like any earlier Tremec. Autotrader link
There are quite a few of these out there with under 40,000, and even under 20,000 miles. By 2005 Ford Mustang was finally catching up to what the LS1 Firebirds/Camaro V8's were doing back in 1998-2002. Some of those cars with similar mileage would be somewhat cheaper than the Mustang.
The gear ratios in 1st (12-1) and 2nd favor the mustang by quite a bit...which also can mean more pounding in those early gears. 1st gear in my T56 Camaro is under 10-1. It still comes down to each particular car and its driver(s) history.