Interlibrary loans are often limited as to the number allowed (a librarian friend told me they are quite expensive for the library, so I tend to save them for things I can't find for a penny + $4 shipping on Amazon) but many libraries are part of a county or regional system so you can get books from a lot of different branches. Most of the branches I have lived near in the last couple of moves have been quite small so I almost always do requests.
Do you have a tablet or e-reader? I ask because, along with the library's e-books, (and sometimes you can borrow from other libraries' ebook collections, depending on state or regional agreements), Amazon and Barnes and Noble have a lot of cheap e-books. Amazon usually has 4-5 on sale for .99-2.99 as a Daily Deal, plus a monthly sale on another 100 or so titles, plus sometimes they will do an extra sale (they usually have a huge Black Friday sale). B&N gives away a free Nook book every Friday. SOme of them are dumb, but some are quite good! Those tend to be cheaper than anything I can find used, other than yard sales or the clearance rack at the local used book store. At this point, e-readers have been around long enough that you could probably pick up an older model pretty cheaply or a lot of people probably have them in the back of a closet if you ask around.