Thanks for sharing that Mike.

What are the 20 essays like? Interesting?
I like to have songs these in book form (even though you can find them online) - just much more browsable and user-friendly I find.

Some other interesting discounted books on that site in the music category on lots of folk related topics (including by Ruth Crawford Seeger and her daughter Peggy's recent autobiography, some quite niche titles on bagpiping too!)