Xamarin For Android and iOS only have "crazy" licensing fees IF you want the professional editions... The Starter edition is free, and their Indie edition is $25 per month: https://store.xamarin.com/.
Yeah, the pricing improved - but essentially, it is impossible to create the same exe for iOS using the open sourced Mono version because of the way in which the runtime is licensed (strict LGPL.) No static linking, so one must buy a commercial Mono license, which would not be the case for this solution.