Dependent on where you live and the volume of salt on the road an aluminized mild steel may do for you and is considerably cheaper than stainless. I used a local muffler shop for my 850R that had a mandrel bending rig and lived with their recommendation as to the size of the resonator and muffler. My total cost was less than half of a stainless system. I live in South Florida where they do not use salt on the roads, they prefer crushed coral :-), the factory exhaust on my Sterling 827 SLi is the original aluminized steel and after 11 years and 182,000 miles is still as good as ever.
John Scales 850R 1996