Only for reading, easily available in EU, low budget: which e-ink device/distro?

I'm looking for something to read books on, copied over from a local collection (mostly .epub). Networking is not desired, a fast USB connection is. A good battery or exchangeable battery would be nice.

Not too large - maximum DIN A5 for the whole device.

I remember from years ago that some devices were deemed unhackable, some much more suitable to install Linux on.

I'd prefer to buy used, so something that was sold a lot in Europe is preferable.

I will not spend much more than €100.

In other words, some old commercial e-reader that was known for being hackable, I guess.

Please do not recommend the new PineNote, it's (slightly) too large and way too expensive and I don't think I need that much computing power.

Thanks in advance.