I have been looking for the same thing a while ago, since I couldn’t afford a Mac as well. But I can tell you: You will not find a solution that is not building on a Mac system. It is really mandatory for all the Frameworks out there (e.g. Xamarin).
Background Info: I wanted to port an app I created in Android Studio (for Android Devices) to apple. The App is about the school I am attending and shows student relevant information (for example: substitutions).
So I came up with the following: I kindly asked some people of the booster club of our school out about a solution for my problem. Surprisingly, shortly after, they gave me a contact to an IT company that was so kind to borrow me an older MacBook Pro (2013). So thats the one I am using right now and it works just fine!
Conclusion: I recommend you to ask around people you know, If they are willing to borrow / cheaply sell you a device for development. Try to convince them about the good cause they are doing, as in my experience it really works!
I wish you good luck finding a solution for your problem but remember: You will not be able to avoid anything made by Apple!