For teachers and educators only, The Scholastic Store offers preorders of the Scholastic 50-Paperback Book Collection for Grade K-2 (pictured) or Grade 3-4 for $178. Coupon code "ZKF" cuts it to $50. With $4.50 for shipping, that's $1.09 per book, $200 off list, and the lowest total price we could find. Deal ends June 30.
It's also available for Grade 5-6 for $240 before the above coupon, $50 after. That's $300 off list and another price low.