You can use ereaderiq to alert you when titles go on sale. I like to have digital copies of books I already own in hard copy, and more often than not those books go on sale for $1.99 or $2.99 eventually. I also buy books that I borrowed from the library if I feel like I may want to read them again for whatever reason. Even if I don’t plan to read it again, I’ll buy the ebook at that price point just to give the author a little boost if I enjoyed it. At that price point you can be a lot more flexible, you just have to be patient.