I think this seller made a typo. I bet he intended to list it at $199. Otherwise, he's on crack.
As for prices, they are determined not only by "rarity" but by "demand". There is a high demand for this game... I'd go so far as to say that it is one of the most sought after titles, simply because there are tons of Castlevania fans who have no interest in PCE, per se, but who would still want a PCE (or magicengine) solely to play the coveted Dracula X.