Ok, I got all aluminum stock I need. It was only 70 bucks too! I was expecting a couple hundred. The 4″ pipe alone would’ve been $272 from McMaster.
The only problem: they only had 4″ od aluminum tube, and only 1/8″ wall. For $40 vs $270 though, it’s worth changing the design a little. After looking at it in person, I think the 1/8th wall will be plenty strong enough.
After I post this, I’m going to go order everything else from McMaster.