I learned Android first then iOS. You should really do both as in my experience, every client that has come to me wants an app on both platforms. To distribute

I learned Android first then iOS. You should really do both as in my experience, every client that has come to me wants an app on both platforms. To distribute on Google Play is a one off fee of $25. To be an official Apple Developer is $99 a year. You can of course just develop apps for jailbroken iOS devices, that won't cost you anything and you can do it on Windows; but if you want to do it professionally then you need to become an official dev.