hellion sells a single.. as well a pro turbo kits, but be prepared to wait forever for them to get one to you
W/o front suspension.. $3900+ shipping W/ front suspension (Qa1 tubular K and QA1 A arms) $4600 + shipping...
Heard good things from these people, would be helpfull if you had acces to a good mustang shop with a tuner. http://www.on3performance.com/