Bargain @ $1.99 from Houghton Mifflin Harcourt's Mariner Books imprint in the US only (some HarperCollins imprint has the rights elsewhere; price should be the same at all the other US retailers):
The Road to Middle-Earth: Revised and Expanded Edition by retired literature professor and Tolkien scholar Tom Shippey (
Wikipedia), his behind-the-scenes exploration and analysis of J. R. R. Tolkien's influences, literary achievements, etc. ETA: apparently this is not only notable enough to have its own
Wikipedia entry, it turns out there's an actual Mythopoeic Scholarship Award in Inklings Studies just for Tolkien stuff, which this won back in the original edition.
The Road to Middle-earth, Tom Shippey’s classic work, now revised in paperback, explores J. R. R. Tolkien’s creativity and the sources of his inspiration. Shippey shows in detail how Tolkien’s professional background led him to write The Hobbit and how he created a timeless charm for millions of readers. Examining the foundation of Tolkien’s most popular work, The Lord of the Rings, Shippey also discusses the contribution of The Silmarillion and Unfinished Tales to Tolkien’s great myth cycle, showing how Tolkien’s more “difficult” books can be fully appreciated. He goes on to examine the remarkable twelve-volume History of Middle-earth, written by Tolkien’s son and literary heir Christopher Tolkien, which traces the creative and technical processes by which Middle-earth evolved.
A previous Tolkien studies bargain is also still $1.99 in the US:
The History of the Hobbit: Mr Baggins and Return to Bag-End