Well, obviously, the library is free...but my local library doesn't have the biggest selection. Plus, sometimes, I like to read a book without worrying about finishing it before it being due. So, how do I buy books on a budget? Well, in the last year I discovered www.half.com - a division of ebay where people go to sell books, video games, dvds, cds, etc. But, there is no bidding war. You put in the title you want and it brings up all the sellers who have it and their prices. So, you can select the price and condition you want. You do pay a flat shipping rate of 3.99 per item, so keep that in mind. But I recently found 6 books on my Newbery list - all excellent condition HARD BACK copies for .75 each! So, even with the shipping, they were less than $5 each for books that were originally about $15 each.
Another place I love to book hunt is thrift stores - particularly the Salvation Army store. Paper backs are .99, kids paperbacks are .49 and hardbacks are 1.99! Today I found 6 Newbery books for .49 each! And 6 other books I had been wanting (including a Jodi Picoult book I haven't read yet!)! My kids find books for themselves too, and I don't have to say no because they are only .49 each!