CowBoom offers the used Amazon Kindle Touch WiFi E-Ink 6" eBook Reader, model no. D01200, for $39.99 plus $5.24 for shipping. That's $5 under our mention from four days ago and the least expensive Kindle Touch eBook reader we've seen. (It's also the lowest total price we could find for a used unit by $10.) Sales tax is added where applicable. It measures 0.34"-thick, features a 6" 600x800 e-ink display, and weighs in at just under 9 oz. It also sports 4GB internal storage, 802.11n wireless, X-Ray (which downloads Wikipedia information along with your books), PDF support, and more.
Note that no warranty is available. This used unit may be missing accessories and have scuffs, blemishes, or scratches.