I bought it used like new from Half.com almost 2 years ago for $28. It's weird that the price has crept up a bit since then. It's not like the game is out of print or hard to find.
A few months ago it wasn't even available at most online storefronts and Amazon had it for above $65 new. I also can't remember the last time I saw a physical copy at a store. So judging by that, I would say that Nintendo really hasn't been producing very many new copies.