RS Rear Valance and Paint matching your car
RS rear Muffler/Tips
3" Stainless Piping
Cut off stock exhaust entirely, custom 3" exhaust (RS Is 3" from factory) from the cat to the new muffler, weld it on, make new hangars and attach everything, wire the actuator to a power source located under the car, wire that to a custom switch you will need to install in the cockpit.
Have rear valance painted to match rest of car
Total cost: 1200 in parts and labor providing the rear valance you buy is already the color matching your ST, if not be prepared to spend another 400 dollars to have it refinished and the rear bumper blended to match.