Remove large video from iCloud Photos
Open Photos.app on your Mac.
Enable the Info panel. Now select the Aubums -> Media Types -> Videos. You will see how much storage your videos are using. Mine are using 250GB.
Select the large video files, File -> Export -> Export Unmodified Orignal For “N” Videos. Save them to a remote location. Then delete those files from Photos.
This procedure would help you keep your iCloud storage usage small and thus keep the cost low.