User1875 postedJust a simple experiment. May be a fair indication of the size of standard runtime libraries since the app itself doesn't do much. All apps have been compiled in Release with standard settings using XCode 6, iOS 7.1, Xamarin Studio 5 and Xamarin.iOS 7.2.3.39.
App bundle size:
Obj C 172 KB
C# 3 MB
F# 3 MB
Swift 6.7 MB