Producing a textbook is vastly more complicated than writing a novel. There were nearly 200 figures. There is an index. The core writing file uses LaTeX via WinEDT (not to be confused with winedit) and MikTEX, with the American Mathematical Society addons, generating figures with Inkscape. It’s also large, close to 500 pages of 8.5 x11″ text. I have now marked the index locations, but now must type them.
On the other hand I still plan to charge $20, and one of the competitors has been seen at $400.
Two of my sellers, SmashWords.com and Amazon.com, have launched special programs asking authors to sell books at a reduced price as a support for our Fellow Americans. I have done this for two of my books, namely
Mistress of the Waves — now $1.00 amazon.com/dp/B008J4NLWI
Designing Wargames – Introduction — now $1.50