I don't know about the cheapest but a popular way is to ....
Have the files on a PLEX server - This could mean hooking the Hard drive to a computer or laptop and DL-ing the free plex server application
View the files from a 4K capable streamer. - Here there's lots of choices. I only know about my own configuration which uses INFUSE on ATV4K but there is also a ATV4K Plex app and many of the other streaming devices have native Plex apps.
Have the files on a PLEX server - This could mean hooking the Hard drive to a computer or laptop and DL-ing the free plex server application
View the files from a 4K capable streamer. - Here there's lots of choices. I only know about my own configuration which uses INFUSE on ATV4K but there is also a ATV4K Plex app and many of the other streaming devices have native Plex apps.