Ohhh wow 
I had not heard anything about your work on this so far. If you need some more seedfunding for this, I’m pretty sure Edgeryders OÜ can fork out 1-2 kEUR for more hardware, shipment fees etc…
That book is actually made freely available as chapter-wise PDFs by the publisher itself (Hesperian). See Autarky Library, item 483. Lots of other books in there as well, maybe you find other relevant content.
That Autarky Library content collection is actually the outcome at my end after @natalia_skoczylas, you and me developed the Kafal Local Media Server idea back in 2015. I rather wanted to go for comprehensive content and as a compromise abandoned the audio format as converting all that to audio is impossible without significant funding. Indeed I found all the content, but it’s only English, only PDF, and not open source so that converting it to anything else (even EPUB for proper reading on phones) is a legal issue. So I got stuck at that point as I can’t find a good way to get all that content to the people needing it. Your approach of sticking to audio and going for a small intervention first makes a lot of sense in comparison …