Microsoft Store has a ton of deals on digital movies and tv throughout the year. The best part is that a lot of their movies are Movies Anywhere compatible, so it can be one of the cheapest places to get movies regardless of your platform. Their deals fall into these main categories:
If you want to grow your digital movie library for free, start by getting Microsoft Rewards. They offer points for doing daily searches on Bing.com which you can use to redeem gift cards. Cash in the gift cards for 1-2 movie purchases a month or even more rentals.