It ought to be easier to get a blank slate of a small device with some compute power and a screen, like the Kindle here, without having to jailbreak something.
A 4.37inch E-Paper in 3 colors is $24, problem is need you to program yourself (they have code sample in python, for raspberry pi), and you need a raspberry pi, case, cables, etc.
Also, these cheap epaper displays are, of course, of lower quality (slower, lower resolution) than an kindle display.