work boxes, have one for each student, when they finish their work they can go to their work box and pull out things to work on that the teacher has placed in there. (lets the teacher assign different things for the student/if they need extra practice in an area) - DIFFERENTIATION!
You can order a box of books from this site for $12.99. They will range from toddler to young adult books. Each box contains approximately 150 books (give or take). You can also order more age/grade specific books, but it costs a bit more. There is now an advisory on their site that due to high demand, boxes may not ship for up to 5 weeks, but for $12.99, that's a small price to pay :)