I had such chargers come with my Cybook and EZReader, as well as a couple of other gadgets (my Palm Pre, my Bluetooth headphones and my Jawbone). I also bought one for my sister to use with her Sansa Clip mp3 player. I think I got it from Amazon for a few dollars. Seriously, $20 is a lot! I mix and match them all the time, except for the Pre, as I was told that was not a good idea. I use the Pre charger for other stuff, though.
ETA: Here is the charger