Most revelatory record finds, price-wise

Not the Beatles or Beach Boys, but a few years ago I got a 3-CD promo box set from Point Music used for $15 containing John Moran's "The Manson Family" (spooky!), Philip Glass and Foday Musa Suso's "Music From The Screens" and Uakti's "Mapa", all very good records. It was marked down because someone wrote on it. When I got home, I realized it was Philip Glass's autograph.....