Not the whole story... Xamarin have a Starter Edition that is free for both platforms; admittedly with limitations (maximum app size, no linking with 3rd party code other than Xamarin provided assemblies and the iOS SDK). Within those limitation, you can publish to the App Store with the Starter Edition (obviously you need a Mac as well for iOS). The Indie Edition drops both of those limitations for USD299 per annum, which is reasonably affordable from my perspective. (Disclaimer: I have paid for the Business Edition; USD999 per annum, which adds the ability to use Visual Studio and a few other things).