I like to get my hands on the cheapest edition I can in the best condition at that price. If the words in the book are the same as a more expensive one, I’m getting a better value, in my opinion. Then if it’s a story that becomes really important to me I might consider upgrading to a “nicer” or collectors version, and keep the old ones as lender books.
I’ve spent $100 on nonfiction physical books on particular subjects (not textbooks). I’m running out of physical space for regular books, so I’m switching to ebooks for most fiction. For them, I don’t like to go above $4.99. I did spend $12 on an ebook recently because I had heard a lot about it. It was terrible.