> As I understand it, Google requires Android devices to have colour screens and, so I've read, won't certify eInk eReaders for newer versions of Android.
Google has gone to great lengths to ensure that a phone without its proprietary libraries and SafetyNet attestation will not be palatable to mainstream consumers. An eReader is not a phone, and consumers do not have the same expectation that it will run every app in the Play store.
Some Boox brand eReaders use Android on monochrome displays, but those are far from the author's definition of cheap at $200+.