Japanese Mario Clash

I looked on eBay to see if I could get a Japanese copy of Mario Clash. Apparently not for cheap. The cheapest one on eBay right now is $50. Is there a reason for this, and why the American one is way cheaper? The rarity guide says the Japanese one is a 4/10, and the American one is a 3/10, but does $30 constitute one rarity rating? I’m just wondering.