I am the developer for Coupious mobile coupons iPhone app and with the amount of time that I spent on that application (v1.0 - v1.5), it was probably a $15,000 - $20,000 investment. However, to be fair, I do admit that I was the only developer working on it and when I started the project, I had never seen or used Objective-C before. Despite that, three months later, it was released so the numbers are probably a little skewed because there was a fair amount of learning going on as well as coding.
However, iPhone competent developers run in the range of $80-$150 depending on their skill and time with the platform. I would say that for a simple application, an app would probably run 2K-5K, a medium complexity app would run 5K-15K and a fairly complex app running 15K-30K. Game applications could be even more.
The reason it is so high is that the skill is fairly specialized and not everyone is able to do it