This very common line of thinking is how books that ought to be 75 pages balloon out to 225 pages, using 3x the words to convey the same amount of content.

Should you not set the price on the value of the content, not the amount content?

If the book enabled you to e.g. create and sell a WebAssembly project quicker or win a big client project that requires WebAssembly then $29 shouldn't be worth thinking about to most developers.

Books aren't priced by the number of pages

I agree. Look for example on book called "Learn WebAssembly" by Mike Rourke which contain similar content on 328 pages and is priced at €16.00, have free preview and code examples

Unless it is of great quality perhaps. But I do agree, it seems like just a bit too much.