The problem with projects is that they begat more projects. I'm looking at the angle iron uprights for the shelves, and I'm looking at the floor in the various proposed locations for the completed unit and decide that some feet are required.
I salvaged these plastic blocks when one of my neighbors moved, he built bird habitats.
A little measuring, a Bridgeport, and an 1/8 inch end mill and I have eight of these. Cut between the lines and I have sixteen feet.