Does it have to be an ebook reader? If not, I would suggest you consider the NEC MobilePro 900. It reads PDF and Word natively so you wouldn't have to convert. The prices on Ebay have been dropping; it almost meets your $100 requirement.
Unfortunately, I'm pretty sure you can't get 12 hours continuous use out of a single battery.
Here is the MobilePro 900 next to a 15" laptop:
http://img355.imageshack.us/img355/9...arativatc4.jpg