I have Kindle Unlimited too and I generally have 10 books in my queue at any one time, which does encourage me to read them so I can free up a slot when I want a new book. I also get emails daily from BookBub which sends me my daily bargain recommendations - books that are often free to buy, or 99 cents, or a $1.99. I'm willing to shell out that much.

Currently reading a book that I think was free at amazon - modern day author but a murder mystery set in 1940s wartime England. So far I'm loving it but that's my sort of book. I'm a huge Agatha Christie fan for example. Of course it turns out it's the first in a series and that's how they hook you in - first book free but if you like it you have to pay for the following books.

I find Kindle works best for me for novels - books where you start at the beginning, read until the end, and then stop. I like it far less for things like diet and health related books where I like to jump around, check out topics of interest, go back and forth, re-review topics, etc. There I like an actual physical book.

Don't think I would ever pay $10 for a book by David Katz, regardless of format. I would perhaps consider taking it from the library. But of course the library is closed now so not currently an option!