The cost of publishing your iOS application on the app store costs $99 every year. Additionally, if your application has a price, the app store takes away 30% of what the customers are paying you to download the application. In case your application is free to download, Apple will not be taking any additional cut beyond the annual fee.
The publishing of the app is approved after the app store reviews your application to make sure it follows all of the provided guidelines, this generally takes less than 24 hours.