With a little imagination, various kinds of puzzles can be created. The students themselves may enjoy making hidden word or crossword puzzles for others. Other types of puzzles could be games based on popular television programs such as Jeopardy, Family Feud, and Wheel of Fortune. Book companies are generous in sending examination copies of their books. Textbooks will give you much background information and can also be used as student resources if you're willing to let them get their hands on your books.
Several companies deal with publisher overstocks and previous editions of books.
Also watch local department stores for book clearances of this type. I have picked up many excellent books at sales like these at costs of less than a dollar. Auctions, flea markets, and garage sales can frequently be great sources of inexpensive resource materials. Many people in a community have books and other resources that they may have had in college and would be glad to donate them to a good cause. Build a resource notebook.