I think the easiest way into PowerBI is to get Rob Collie & Avi Singh's book, and to start playing. The book is only about $30, but absolutely worth it.
 PowerBI Desktop is free... Not sure what MS is doing with licensing right now.

To me, PowerBI is much more about data exploration than reporting (which is what SSRS is good for).  You can download PowerBI and play with it at home. If you have a free version of SQL Server available, then PowerBI is great... It's one of the points Rob makes in his book - when you have  PowerBI and a good backend database, you're golden.

You can download both PowerBI Desktop and SQL Server 2016 for free from the MS site.