In today’s Microsoft Build 2016 event, Microsoft's Scott Gu just announced that Xamarin will be available in Visual Studio family WITHOUT extra cost, even in the free edition of Visual Studio Community and Visual Studio Code. Xamarin Studio for OS X will be free as a community edition.
Also, Microsoft announced the Xamarin is open source. it will be one project of Microsoft’s open source family .NET foundation.
Please read more info from Xamarin official website.
Microsoft just announced acquiring Xamarin in end of last month.