Great Britain
William IV gold Proof Sovereign 1831 PR64 Deep Cameo PCGS, KM717, S-3829, WR-261. A scarce type that does appear at auction a couple of times a year, and so is available if one is willing to pay the premium that it commands. An example that emphasizes its originality, there is light red toning and the sort of look that one expects of a coin that was carefully kept in a coin cabinet for over a century. For the sake of completeness, one does notice some light hairlines in the fields, but they are only visible under magnification; when viewed normally, the eye is distracted by the flashy surfaces that stand in stark contrast to the frosted devices.
Estimate: 12000-15000 USD