You can try flea markets and auctions too, and I've seen them at a Used Office Furniture place. I've never paid more than $5 for one (I've only bought a couple). But several years ago, the elementary school here put a bunch of them out on the lawn when they were clearing out for new stuff. Ostensibly, they were to be taken to the school district warehouse (which you could try, too), but really they didn't care if they "took a walk and didn't come back". So a friend of mine loaded up about twenty, and gave them to me when we were starting up our little school. I really have more than I can use, so I'm going to sell some. For $5.