If you want something with a backlight--ever consider an Asus EEE PC? The price tag is still sort of heavy ($300 for the cheapest model), but you get a very portable computer and a backlit (is that the right word?) screen.
I don't think I'd like to read a book on the screen--but then again, I'm not a fan of the backlighting.
Edit: Also--if you're looking for both a backlight and a low price tag:
http://www.ebookwise.com/