I walked past Second Story Books on Dupont Circle yesterday and saw this copy of The Art of Cartooning, usually a $10 book at best, for $1200.
As you can see, it's signed by several cartoonists, some of whom have passed away such as Ziegler and Fradon. Still, you could almost recreate this today.
Instead I spent $4 on Robert Osborn's How to Shoot Quail from the outside selection. It's beat-up but I enjoyed it.
Next to the Cartooning book was an early, perhaps first edition of the Star Wars novelization for $50.