I'd build frames from unistrut, which is easier for those with a chopsaw, instead of buying, borrowing or asking for a welder.

Unistrut cost + strut hardware + chopsaw + square, grinder to clean up edges versus welder, consumables, gas, gauges, learning how to weld.

You can get away with not using a grinder, if you're comfortable cleaning up cut ends on the chopsaw.

I've build a few unistrut work benches, they're still standing and haven't gotten loose from the years i've worked on them. I would do some serious CL browsing for used toolboxes.