After much Zen meditating (or as normal people say, drinking beer), I've decided aluminum framing is the way to go.  Cheap(ish), zero welding, 1 bar should be enough to do the entire structure and then some, connectors are there, connectors are there to reinforce too.  Mounting brackets for everything.

Basically, it is perfect.  Now I get to buy a drill press and band saw for my apartment too.  Power tools, every man's weakness.