The price starts at $300 per person per platform per year, and that applies to you right now should you decide to build anything that involves more than a few kilobytes of code.
Nobody's going to pick up Xamarin for fun, for experimentation, for learning, for scratching a creative itch. You can't download it for your kids or recommend it to your students. They have no product for use outside of companies and that guarantees it will be and die a niche riding on companies not wanting to retrain their .NET developers for iOS and Android.
Earlier this month I got to choose between Xamarin and everything else, I have years of C# experience and I like their IDE for general c#-on-mac stuff.
Does not seem very niche to me.