Mary Stewart: Her Arthurian Legend series. The Crystal Cave, The Hollow Hills, The Last Enchantment, The Wicked Day. If you really love the Arthurian/Merlin legend this one is for you. These books are not in e-book format, but should be in most libraries or can be ordered. Paperbacks on Amazon are fairly reasonable. Used book stores might have them too.
Mary Renault: For Greek history lovers: The King Must Die. A trilogy on the life of Alexander the Great: Fire From Heaven, Persian Boy, Funeral Games. There are some other books like: Mask of Apollo. . These are available in e-book, but not for unlimited. Again should be available in libraries or ordered, paperbacks on Amazon are reasonable, might find these in used book stores.