a very basic 6 foot long x 2 foot x 2 foot structure with a 2 foot angled support from the bottom of each leg to a point intersecting each 6 foot long member would require 32 feet of tubing.
If you chose 2" square structural steel tubing with .187" inch wall thickness it would be 4.3lbs per foot. Total weight of 138 lbs. I currently pay $0.78 per lb. That would mean $107.38 for the tubing at my cost. It would need to be cut, fixtured, welded, ground edges for safe handling....