it's on your itunes settings (also on the store settings of the device). Check the description of the game on itunes store it has all the info about it.
And yes I know I may lose lot of people but it's better than losing ALL the people. If I don't have income to pay for servers, improvements and such, I would have to shut down the game and all gone. So $2 a month (a bit more than a can of coke?) for unlimited playing hours I think it's fair enough.
Think about it, most likely you spend more than that on other games you hardly play or play for a very short period of time. I didn't try to turn rich with this game, I've left it as cheap as I can possible afford