Amazon still has many many School Zone kids’ books on sale for only $1.40. Get FREE shipping with a $25 purchase or with Amazon Prime. Plus, many of the books are part of the 4-for-3 promotion (basically B3G1 FREE).
During the summer, I let my boys play (a lot), but we also try to do workbooks to keep up on our skills (like writing, reading, math), and these are an inexpensive way to stock up. Or, they might be a good preschool homeschool resource.