An e-ink reader capable of rendering full-size pdfs would be ideal, as the reading is obviously all online, but they're still a bit pricey. The most robust solution seems to be continuing to cycle through disposable reconditioned (< $50, usually) kindles. Not catastrophic if stolen, and it renders the text. Sufficient is the device. And for octavo texts (before the modern sizing took hold), it's close to scale.
