In Lancaster I visited the campus Waterstones and bought a book by Chris Grey described as "reasonably cheap". That is almost £15 for a short paperback. But then I realise this is cheap as compared to other academic product. I am interested in the Network Learning Conference and the proceedings may have additional content or guidance. But looking at the Springer website I find that such a book could cost around £70
Sustaining TEL might be about sustainability but finding a public audience for such concerns might include some cheaper options. this may not be the full text but some sort of manifesto or explanation of change in a manifesto could be short and public and free.