Walmart offers Bill Martin Jr.'s Chicka Chicka Boom Boom Board Book for $2.05. (Amazon charges the same with free shipping for Prime members, although it has a stock date of April 21.) Choose in-store pickup to dodge the $4.97 shipping fee. That's $2 under last week's mention and the lowest price we've seen. (It's also $5 below the lowest shipped price we could find elsewhere.)
Update: The price has increased at Walmart; however, Amazon still offers it for $2.05 with free shipping for Prime members.