Update: These holders are not that sturdy when heavier items are placed in them, such as thicker magazines. And there's a gap in the front of the holders because of the size of the box. But if you can find smaller boxes, the same concept would work.
I used post office boxes that I had left over from sending other stuff. You can use any kind of box about the same size. Suggestions have been cereal boxes, reuse boxes you have around the house or whatever.