Amazon offers downloads of Randall Munroe's What If?: Serious Scientific Answers to Absurd Hypothetical Questions Kindle eBook for $2.99. That's $22 off list and the lowest price we've seen for this book in any format.

Also available is Randall Munroe's Thing Explainer: Complicated Stuff in Simple Words Kindle eBook for $2.99. That's also $22 off list and another low.