I'm sure others have already seen this happen, but it's the first time I've noticed it. Today I ran across a book that is no longer in print (or at least not available on Amazon), but is still available as an ebook --
They Say, I Say. The nice thing is that this is an accademic book and new versions of the book (from sellers other than Amazon) are going for $45+ and used versions of the book are going for $15+. The Kindle version is $9.99.