The PRS-350 from
Dell at $129 is a better deal on a 5" Sony. The 350 is definitely worth an extra $30 over the PRS-300, and is the best 5" EInk device at present.
If $100 is your limit, then the Nook WiFi is a good deal. The basic design is a year old, but there is a software refresh coming soon and it may have already improved over when you tried it.