You can develop iOS apps in C# using Visual Studio on Windows with Xamarin, using none of Apple's development tools, as I do. Visual Studio is free, until you hit $1mn in annual revenue or have >250 developers.
Apple requires you to run remote builds on a Mac, so even if you don't plan to use their development tools at all, you need to have a Mac somewhere to act as a build machine. Then of course you need to pay the annual Developer Program fee.
According to reports, Apple has around 20 million developers. If true, that implies the Developer Program fee alone is bringing in $2bn annually.