Woot (an Amazon company now) has "refurbished" (marked "used – good") Kindles and Fires for sale again. Starting from $20 ($15 + $5 shipping) for the Kindle 3 (Keyboard) and up to $55 ($50 +$5) for a Paperwhite 2 (and several others in-between). The $5 shipping is for the entire order, so if you buy multiple devices (or anything else Woot sells) everything ships for $5 per order. Fire tablets (HD 6) start at $25 ($20 + $5). All Amazon devices appear to have 90 day (Woot limited) warranties and ship directly from Amazon.
https://www.woot.com/category/comput..._cnt_cdet_pc_4
(If this link quits working – like the last one did? – just go to Woot.com > Computers > Tablets.)