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.
The most I was willing to pay apparently was $325 in 1995 or so for a single textbook. After that, the leather bound edition of The Tales of Beedle the Bard but I can’t remember how much it was. (If anyone remembers I’d like a reminder)