Apologies in advance if this isn't helpful...but I can think of a simple two-device combo that meets your needs and comes in below $300 if you don't mind the inconvenience of carrying two devices.
1) Your favorite e-ink reader below $150.
2) For writing, how about an AlphaSmart Neo? (
www.Neo-Direct.com).
It is a great portable writing device, full size keyboard that is wonderful, six-line screen (there is an unofficial download that enables 8-9 lines on the screen), runs on 3-AA batteries for **400 hours!!** and designed for the education market, so it is quite durable.
I've had my Neo for about two years, have owned all three AlphaSmart devices and they are durable, incredibly reliable and easy to use. Highly recommended!
The Neo stores up 80,000 words in internal memory. (My main gripe with the Neo is no USB or smartcard storage...that and a slightly larger screen would make this a PERFECT device).
When you get back to home base, just connect your Alphasmart to your PC by USB cable, open up your favorite word processing software and hit the "Send" button on the Alphasmart -- it sends your files to your PC as a text stream (your computer just thinks it is a keyboard and you are typing really fast) -- so no special software to install.
The Neo is aobut $150, but there are a couple of new ones on Ebay for $80.
The Dana is a palm-powered device, great keyboard, but it chews through a set of AA batteries in only 30 hours so bring spare batteries. Screen is difficult to read unless you use the backlight...but still not a bad choice, especially since you can get them used on Ebay for about $40.
If you want more info, check out the
Alphasmart thread on Flickr.