What is the value of a 1939 nickel with no mint mark?

Prior to 1979/80, coins struck at Philadelphia didn't carry mint marks*, so your nickel comes from that mint. Please see the Related Question for value information.

(*) So-called "war nickels" bore the P mint mark from 1942 to 1945. The first coin to regularly carry a P was the 1979 SBA dollar. The next year, all other denominations except the cent were also given P mint marks.