Why don't you repurpose cheap e-book readers, such as Kobo, which run Linux? https://wiki.mobileread.com/wiki/Debian_Linux_on_a_Kobo or BQ Cervantes: https://github.com/bq/cervantes or you can root the Nook e-reader running Android or you can check out the Open Book Project: https://github.com/joeycastillo/The-Open-Book