Who needs an Amazon Kindle when you can build one yourself? The Waveshare e-paper HAT comes in numerous display sizes ranging from 1.54-inches to 9.7-inches. The HAT communicates with a Raspberry Pi via SPI, UART or USB depending on the model and comes in a choice of two, three or four supported colours. The Waveshare e-paper HAT costs between US$15.99 and US$169.99 and ships worldwide.
https://www.notebookcheck.net/Turn-your-Raspberry-Pi-into-an-e-reader-with-the-Waveshare-e-paper-HAT-an-expansion-board-that-starts-at-US-15-99.421477.0.html
Too bad this is not a touch display. It would be very close to low power tablet, which would be more universal.
Unfortunately it appears that the display can't be set as an active one and only displays bmp...