Cowboom (Best Buy's outlet site) is selling the
Sony PRS-350 for 39.99 + 5.00 shipping + tax, as their deal of the day. I bought one from Cowboom through their auction site, and it was in fine condition. I think it's a great price for a really wonderful, pocketable reader. If you don't mind bidding, you can usually find them through Cowboom's auctions
here, starting at $24, and I rarely find more than 1 bid for any of them, so I would guess you can beat the deal of the day price, if you're patient.
Please note, these are pre-owned (which means they could have been display models, or returned product), but they have been tested to work. Plus, Cowboom has a 30-day return policy, postage paid, which I found very easy to use when I got a nook color which I didn't like.