I did a flexi rack variation with 2x2' plywood, 5/8" threaded rod. I used 4 posts, and covered the threaded rod with painted PVC pipe.
I used a jig to cut the pipe in even lengths for each shelf, which made spacing easy. I ground a point on the 4 ends of the threaded rods,
threaded on a double nut, washer, and rubber spacer. I stacked the shelves on each other, drilled the holes through all of them so they would line
up the same. I sanded, stained, and put edging on them. On goes the bottom shelf, a rubber spacer, a washer, and a nut. Wrap a tight warp of
electrical tape on the 4 rods, slide on the painted PVC pipes, and repeat. I used rubber insert nuts on the top and cut the rods off flush.
Also, all the washers and nuts were painted black. Not high end, but cheap!
But in the end, I've seen some pre-made racks that were just as cheap used. This one is deeper and wider than most. I have been thinking
of re-doing it with some better shelving. I have already shortened it, changing some of the shelf spacings. In the end, not too bad.
This photo could be better, but it gives you an idea on how it works out.