Resonant Serpent
Since you already have the book in PDF form, it wouldn't take much to add it to Amazon's Print on Demand service. You supply the digital file, and they print the books as needed. You wouldn't have to buy a stock of already completed books, and the cost for wholesale books is reasonable. My wife uses it for her fiction, and the turnaround between requesting books and getting them delivered has always been quick.
https://kdp.amazon.com/en_US/help/topic/G202059560
Thanks for the tip, I really appreciate it. Based on what I saw in the link, though, you have to do a "real" publishing deal with them, and also it's Kindle-only Printing costs are deducted from royalties, it needs an ISBN number, etc. Although I certainly hope CbB does well enough to justify putting that kind of effort into doing a book, at the moment I don't know the extent to which Cakewalk would support it, and to spend time marketing and promoting it might not justify the effort.
The main reason I did it was because the reaction to the first two books was so positive I felt I needed to at least replace them with something that was CbB-specific. Of course I hope to at least cover my costs, and wouldn't mind making some money from it; if the situation warrants it, I'll look into doing an actual book but hopefully, the PDF will serve most people well enough.
If you have a minute, I'd like a PM about whether your wife thinks doing her self-publishing is worth the effort. For all I know she writes best-sellers and is buying a third house in the Caribbean :) but I do know it takes a lot of effort to make the world aware of a book, particularly fiction where there's so much competition. At least I don't see many 400-page Cakewalk books out there competing with this one!