By far the biggest cost consideration is time.
CGP Grey said in a 2013 Q&A (YouTube video, transcript):
I've tracked my time to get an accurate answer and every minute of final video you see takes me between 10 and 20 hours of writing and animating to make. So a typical 5 minute video is 50 to 100 hours of work.
While that's a lot, it doesn't include the research phase which is difficult to quantify -- some of the videos I've made I'd been collecting notes on for more than a year before starting.
Note though that CGP Grey is a one-person production studio. Moreover, he seems to be a perfectionist and his videos are IMHO very good.
Many other video courses I've seen put in much less work. It seems to me that some (e.g. Salman Khan) do an impromptu, one-take recording. One tradeoff is quantity vs quality - CGP Grey has 88 YouTube videos in total, while Khan has thousands.