I spent $17 on old books today. $5 at the Princeton Theological Seminary Book Sale (it was Box day.... $5 per box, provided you have to be able to carry the box out of the place, otherwise they'll charge you for two boxes) and $12 at the Wellsley Book Sale (which boasts to be the largest used book sale on the East Coast... I don't know if that is true, but it is certainly large...)
I managed to get a First Edition Umberto Eco, a $25 copy of Hemingway's Old Man and The Sea from 1952, a Vonnegut, a copy of Franny and Zooey that appears on Abebooks for $59 and a really neat old copy of "The Autocrat of the Breakfast Table" by Oliver Wendell Holmes. Not to mention an Oxford edition of Jonathan Swift, for the Husband. Over all I got more than 30 books for $17 total!