A very 'hip' young friend suggested that I might want to check out LibraryBin. You might want to check it out too, if you want to support your public library even while you are purchasing materials. The site states, "The proceeds of each sale, after deducting the payment to the publisher for the wholesale cost of the title plus a hosting and fulfillment fee, are donated to the participating library that you specify. These earnings can be used to purchase eBooks, audiobooks and other media for the library’s download website."
Unfortunately my library does not belong to the Midwest Collaborative for Library Services but these libraries do: Albion District Library; Ann Arbor District Library; Brandon Township Public Library; (Lansing) Capital Area District Library; Chesterfield Township Public Library; Fremont Area District Library; Grand Ledge Area District Library; Grosse Pointe Public Library;The Hastings Public District Library; Howell Carnegie District Library; Kalamazoo Public Library; Kent District Library; Loutit District Library; Orion Township Public Library; Plymouth District Library; Portage District Library; Royal Oak Public Library; Salem-South Lyon District Library; Spring Lake District Library; Sterling Heights Public Library; Troy* Public Library; Warren Public Library; and (Battle Creek) Willard Library.
*Noted in another post that this library is Closing.