You should look at the
E-book Reader Matrix. The only older device (not on that list) you might consider is the PRS-500, older screen technology and no support for Secure Adobe PDF and ePub but lots of readers here are happy with it. Another possibility is the Jetbook, sold at Fry's, but that isn't EInk.
For $299, Books on Board sells the Bookeen Cybook and Astak sells the
EZ Reader, which is a Hanlin V3. So the PRS-505 is your cheapest new EInk device option.
With any device, you will probably need Calibre on a Desktop PC to format shift ebooks to the format prefered by the device.