Columbine (briefly) 55% off at Amazon
The expanded edition of Columbine is 62% off at Amazon right now ($7.60). (Update: now $6.43, for a new copy.)
To be honest, I have no idea who sets the discount there, or how or why or when. So I have no idea how long the sale will last.
(It's typically about $12 or more online. The cover price is $17, which you pay at most physical stores.)
Update Aug 16: It was 50% off when I posted this, but it dropped to 62% off. I updated above.
