I'd like to recommend using the auctions from Cowboom, which is affiliated with Best Buy. I purchased a Sony PRS-350 via auction for $39, which was in mint condition. There are several Sonys available here under $60, including the highly regarded PRS-950 for with no current bids for $55:
http://www.cowboom.com/Computers/iPa...grid&keywords=
These are not new, but I've found them to be in excellent condition, and Cowboom allows you to return the device within 30 days at no cost (which I used to return a Nook Color which I didn't like).