I just spent a few days making this shelf system for my scrap desk. Lumber isn't cheap so I rummaged around in our shed to see what I might find to make it with. It's not beautiful, but it works well and still a better bargain than the particleboard cubes they sell in the craft stores, even with what it cost me for the shelf uprights, clips, and paint. (Though my paint job leaves something to be desired. I hate spray paint!)
So... I took apart a bookshelf my husband had picked up somewhere, which was painted blue. I used the shelves, which I cut down, to make the sides and divider. The top piece of wood was grabbed from my mother-in-law's house and sitting in the shed. The bottom was a salvaged piece of low-grade plywood. Had an ugly black grease or oil stain but I primed over it well. Most of the shelves were also cut from low-grade plywood but one side doesn't look so bad. (The other side wasn't so good though.) There was another piece of plywood that was better quality. Enough to make one of the longer shelves and a bit left over to make a shorter shelf. And a leftover scrap of the wood I used for the top I used for the other short shelf.
If you can't be rich, you might as well be handy. LOL Click the photo if you want to see it larger.