Someone in another thread mentioned Speedy Metals and they’re definitely the cheapest I’ve been able to find. For whatever reason, the .065 wall tubing is 1/2 the price of the .049, so that’s what I went with. Tubing for a 24″x36″ machine was $100.60 including tax and shipping to Detroit.
Edit to add: This tubing is tough! Don’t try and de-burr it with an emt deburring tool, it’ll get eaten… I had to use the grinder and a file to get it nice and clean.