Pixar have made RenderMan free for Non-Commerical use and have dropped the prices on their amazing render engine. NoFilmSchool have a good overview of the opportunity, to Hone Your VFX Skills for Free. The thing I find interesting is that it’s not really free, since you are investing time in their render engine as apposed to other renders. However, it does provide the opportunity to access RenderMan and build up a demo reel.