I went through this process a while ago. Everything from books on Casino management (fascinating topic), a skyscraper building company, running a private university, and the perfume industry. I’ve got hundreds of books titles I can give you that aren’t reasonable to type here. PM me for more info.

Best general advice I can give you is to go https://thriftbooks.com. A better selection than Amazon at prices 70% less (assuming the books you’re buying are at least a couple of years old).

Just start typing in random names of topics (or industries) you’re interested in and go crazy.

I’ve bought about 3,000 hardcover books from them with an average price of $3.50 (and that’s including tax and shipping).