Square Enix has released Final Fantasy III for your iPhone, iPod Touch and iPad. The publisher is known for charging silly amounts of money for its mobile games, but this may have broken the record -- Final Fantasy III iOS will set you back $15.99.
If there's a more expensive iOS game, I don't currently know about it. The last game that I remember boasting such a price was the iPad version of Chaos Rings -- published, unsurprisingly, by Square Enix. That originally sold for $15.99, though it's much cheaper now.
So far the game has positive reviews on iTunes, so nobody's balking at the price yet. On the bright side, Square Enix has reduced the price of a bunch of other games, so get those while you can. Some of them are priced sensibly now.