A copy of Diamond Trust of London, in which two players compete to get the most diamonds out of Angola in an eight-month period, will run you $30 (plus shipping). It's definitely a niche title, more or less a board game enhanced with the ability to reveal information to one player without the knowledge of the other. According to the game's official website, there are still over 4000 copies available as of the time I'm writing this post.
If you're interested, try not to tarry. I wouldn't be too surprised if it sells out just because it's an inventive concept from a clever dude. Hell, I bought one.