What is the value of a Thomas Jefferson 3-cent stamp?

According to Hobbizine, a mint version of the 1938 Thomas Jefferson 3-cent stamp is valued at 40 cents as of September 2014. A used version of the stamp is valued at 20 cents.

Over 130 billion Thomas Jefferson stamps were printed from 1938 to 1939. The pale to dark violet stamps were widely used through the 1950s, since a single stamp could mail a first-class domestic envelope from July 1, 1932, until July 31, 1958. One 3-cent stamp also paid the international postcard fee, which was in effect from July 9, 1934, until July 31, 1958. The stamp also could be used in mailing letters to South America and Spain, which cost 3 cents per ounce between Oct. 4, 1932, through Oct. 31, 1953.