Rhythem heaven was 9.99 at amazon over Xmas. I bought it and didn't like it, its a really stupid and almost unplayable game. But I downloaded a save (I have a gameshark that lets me backup and download saves to my carts) with all the games unlocked so I should be able to get at least some enjoyment out of it through that.
I think I will really like fossil fighters but I have a ton of games now, so I will just wait for it to drop further or buy it used when it gets cheap. I definitely think this one will drop further.