For $125 you can get a Zodiac 2 which a very good e-book reader. It doesn't meet your sub-$100 requirement, but I recommend you consider how much PDA you'd get.
http://tapland.com/news_arc/?id=653
You get a hand-picked Zodiac 2 with charger, sync cable, software CD, and other stock accessories, as well as a "spare" Zodiac that was returned for repair and that is used as a rear-cover donor.
Some of the Zodiac 2's finer points:
128MB internal memory
huge battery
Dual SD card slots
480X320 hi-res color screen with virtual Grafitti area
Stereo Speakers
Bluetooth