What is the value of a 1964 mint condition nickel that was not preserved?

Well, if you get it certified as Mint State-65 with Full Steps by one of the major third party certification services, it would list (retail) at $55 with no mintmark or $500 with a "D". If it has not been preserved, I doubt if it would quite meet the standards for a Mint State-65 coin, however if it did, but did not have full steps on the reverse, it would catalog for 50-55 cents retail. Certification will cost you about $40.