Just a note to DIY builders here. Many larger cities in the U.S.A. will have a Surplus Steel or Surplus Metals company in town. Surplus doesn't have to mean old rusty or used crap at all. Usually it's brand new leftovers from large jobs.
Both surplus places I've used in the last 10 years had top quality steel and alloys that were well protected from inclement weather. Maybe a light surface rust on some but that's no problem. The two I've used sell by the pound, not the steels specs, and the prices are jaw drop low! In general I can buy $500 worth of steel for $50-$100 or less.
Added bonus is some of the premium stuff is often mixed in with common mild steel and is sold at the lower prices. Just have to check the numbers on the tube, plate or whatever and know what you're looking for. Pays to investigate and shop around.