There is a Windows PC, there is an iPhone.
What other minimally expensive equipment is needed to write software for the iPhone?
As such, the programming language (objective-C, C#, etc.) or the development environment (such as Xamarin) does not play a role.
Officially, the iOS SDK (development kit) is only available under Mac OS X, and it, in turn, is officially only available on Macs. To build any applications, unfortunately, it will be required, including for building applications based on Xamarin, Unity – all these frameworks only create projects for XCode, which already need to be built under Mac OS X.
The cheapest Mac Mini in Russia now costs 40990 (it also needs a monitor). As another alternative, you can look at Mac rental services like MacInCloud (didn't use it myself though). You are given remote access to a Mac, on which you can already build the application.