I suggest devices that support FBReader. You can get FBReaderJ for Android, but this is the original FBReader for Linux. For example, EInk devices from PocektBook and Boox and 5" LCD devices from JetBook. In the US,
Dunlin's Books sells a selection and so does pocketbook's web site. These unfortunately tend to be a bit more expensive than the devices from booksellers. However, I see that Dunlin's currently has a Boox 60 (with the discontinued older screen) for $99.
The JetBook Mini isn't E-Ink and is has no WiFi, but it is a pure non-DRM play that only reads the FB2 ebook format - with all other formats "supported" by the owner using Calibre on a PC/Mac to convert to FB2. The Boox and PocketBook EInk devices support Adobe DRM via Adobe's reader software but also include FBReader for many DRM-free ebook formats.