How about Nook Simple touch. (run android but u need to root it to be able to do more)

Cheap :-)

Battery:
2 months with Wifi Off
3 weeks with Wifi on. (i suppose moderate usage)

Supported file formats include EPUB (DRM and non-DRM), PDF, JPEG, GIF, PNG, and BMP

source: http://en.wikipedia.org/wiki/Nook_Simple_Touch