There's an aftermarket OS called Rockbox, which is mostly intended for music (obviously). But it remembers the last played track and position so it also works well for audiobooks. You can check it out here:
https://www.rockbox.org
Supported devices:
https://www.rockbox.org/wiki/TargetStatus
I use this with my Surfans F20, a (relatively) cheap HD-Audio DAP.