Although this item is indeed rare (Though not as über-rare as previously suggested, I have seen it up for grabs a few times in the past 5 or so years), there are still other items that are considered
Holy Grail of Castlevania calibur, such as the unreleased SotN demo cartridge for the Game.com, or this:
(and this particular version is unique from all the others due to a special contest Konami held way back in the day, not just the gold plating)
Let me know when any of these are up for sale