The ranges are all over the place. But I would say for a competent developer they start around $50 per hour. Under this rate, and especially at the lowest rates, quality becomes a gamble. You might be able to find someone competent living in a country with lower costs of living, offering a lower rate, but usually if they're good, their rates will just be slightly lower, especially since iOS development is such in a high demand now.
There's a post on StackOverflow (
http://stackoverflow.com/questions/209170/how-much-does-it-c...) that contains a lot of information about what it means to build a quality application, and that will give you some idea of the time frame you can expect. There are also some mentions of websites where you can look for hire.