Many university and public libraries subscribe to Kanopy, which is a great streaming resource for feature film. Making sure that the films on your curriculum are available to stream on Kanopy is one way to help students access the required viewing at no cost to them. Different institutions can have different types of subscriptions, so make sure that students all have comparable memberships through the same institution, if possible.
If you plan on requiring students to view films on commercial streaming services, like Netflix or AmazonPrime, there are several regularly updated guides to keep you appraised of what's available to stream on these sites. Even if you aren't requiring students to have a subscription, it might be a good idea to consider whether a film you assign for home viewing is available on a commercial streaming site so that students won't have to choose a pay-per-view option. The ubiquity of Netflix, in particular, can work as a sort of insurance that a good portion of your students will not have to spend extra money to view the assigned film.
**Note: If students are required to have a subscription to one of these services for your class, YOU MUST COMMUNICATE THIS and state it as a course fee. DO NOT assume that all of your students have a Netflix account.
If you are requiring students to purchase a film to view, make sure that the required film is easy to purchase. Check Amazon Prime to Buy or Rent, Google Play, and/or iTunes to see if the film is available to digitally rent or buy for a reasonable price.
If you are assigning films from a streaming service in your online or distance learning class, check to see if you have any international students! Streaming rights and licensing deals vary from country to country. Just because a film is available on a service in the U.S. doesn't mean it's available in another country. Please be aware and mindful of this when assigning students required viewing accessible only through a streaming service, especially a commercial one.