Current 409 Stainless Steel Sheet prices by dimension, with $/lb for cross-size comparison.
409-Cold Rolled Sheet is currently $2.15/lb.
About 409|A ferritic stainless with only about 11% chromium, stabilized with titanium. This is the exhaust system stainless. It handles high temperatures and thermal cycling well at a fraction of the cost of austenitic grades. It will rust on the surface in humid conditions, but it won't fail structurally. Machines easier than any austenitic stainless since ferritic grades don't work harden the same way. No nickel means the chips break better and the cutting forces are lower. Not commonly seen in machine shop work since most 409 applications are formed and welded, not machined. Compare to
430 (more chromium, better general corrosion resistance, takes a nicer finish) and
304 (far better corrosion resistance but significantly more expensive).