Currently you can stream Manakamana via Kanopy, a streaming service that you can access through your library or university. If you don't have access to Kanopy you can also stream the documentary via Fandor. You can access Fandor via Prime Video, we've included a link to the page above.
If you don't have access to Fandor or Kanopy, you can buy or rent Manakamana from either Google Play Movies or YouTube. This will cost you at least $3.99.