If your child's school participates in the Scholastic book flyer sales, I highly recommend buying the 95-cent books that are frequently available. Sometimes the books aren't that great, but sometimes they are quite good. I got a paperback version of the Chicken Little book pictured here for just 95-cents.
The best thing about 95-cent books is that they make a great birthday "card." Just write a message on the inside cover. Ninety-five cents is cheaper than almost any birthday card you can find in a store, and the book won't be looked at and thrown away after the thank-you card is written.
You can purchase the hardcover version of the Chicken Little book depicted at Amazon.comfor $4.00 (affiliate link). Or just keep an eye out for the deals in the flyers - they sometimes repeat!