How much for 2.5 dual exhaust on a Duster

Right at the moment it has a 360 Magnum right out of a stock 95 truck 20k miles. All that I have done is change to carb via mopar dual plane manifold and a electronic dist headers elde carb. I even kept the serpetine belt setup. Down the road I will do some mild motor work or maybe start from scratch. It is amazing how well this motor runs with a carb. I am going to let the muffler shop do the X pipe. I have heard lots of good things about this particular shop. I figured I would go for the 2.5 now as it shouldn't hurt to much if at all. It just for weekends stop light to stop light and maybe a trip down the strip once or twice.