Ebay via Bundle.com
Price tag: $1,740
A comparative bargain compared to the rest of the items on the list, this super-rare textbook offers a glimpse into some mankind's greatest minds. From Galileo to John Locke, full biographical writings about the lives of revered philosophers lie within as well as articles about ancient philosophy and the German Enlightenment.
But don't worry Mom and Dad. College textbooks (usually) don't cost quite that much.