As of today, Prime31’s Window plugins for Unity are free!
Thanks to a deal between Microsoft and Prime31, you can get FREE Prime31 Windows Store and Windows Phone plugins until July 2015.
Also, Fortumo is offering up to $25,000 for you to implement their carrier billing in your Windows app!
You can read more by going to "Get free Prime31 plugins, plus $25,000 Fortumo offer!" on the Tobiah Marks blog.