Amazon has popular kids' boxed books sets on sale for as low as $16, plus they are eligible for a Buy 2 Get 1 Free promo (add three sets to cart to see discount), making three boxed sets as low as $32 with free shipping.

Search "box set" to see all available options in the B2G1 Free promo; some great titles in this sale!

As an example, you can get the Harry Potter Hogwarts Library Boxed Set ($21) + the Teen Titans GO! Box Set ($19) + the His Dark Materials Boxed Set ($19) for $59 - $19 off at checkout = $40 shipped for all three boxed sets.