Need game developed for iphone/ipad

Good Day,

Please give me an indcation of price and estimated time to develop game. A game which will be for iphone and ipad. I already have the idea and someone who can help with graphics.

One main criteria is that like facebook games people can download for free. But if they for example want a different weapon, or want to level up quicker, they need to buy credits with real money to get the items.

I look forward to all bids. If you have any questions by all means.