Ron Guth:
1865 saw another drop in the mintage of Quarter Dollars at the Philadelphia Mint, this time down to the lowest level since 1827! Even so, the 1865 is not recognized as a rarity at all because sufficient examples exist in all grades up to MS63. Thus, the combination of a small mintage and a low price makes this an unappreciated sleeper in the series.
Above MS63, the 1865 Quarter Dollar is very elusive and the prices rise dramatically with each extra grade point. The finest example is a single PCGS MS67.