http://www.techradar.com/news/amazon-prime-video-may-soon-have-a-free-tier-with-ads

Amazon is a little late to the world of on-demand TV streaming, but AdAge reports that the massive online retailer is trying to catch up by developing a free tier for its Prime Video service. 

Much like the least expensive version of Hulu (or, you know, regular TV), the potential service would be supported by ads.