An insert poster is a 14x36 inch cardboard image theaters once placed in display cases, a practice long gone.
Illinoian Keith Johnson bought the vintage poster as a teenager for about $3 at an antique shop in 1968 or 1969. He kept the poster because he is a horror film fan. Some 30 years later he and his wife wondered if the thing had any value other than being a super-neato image of Boris Karloff as Frankenstein.
Turns out Keith's little gem was a small goldmine. The poster was the only one left and someone else wanted it real bad, man. Like so bad they coughed up the price of a small house to take it home.