If you're grabbing 720p of things you actually watched, then at 4 hours at day and 1.5Mbps an entire year of recordings would be less than a terabyte. So I'd estimate this as a $1-5 per month hobby and the time/effort shouldn't be too bad either. If they reach small NAS territory then that's a useful thing to learn.
Just yesterday, I was watching Digging The Greats on YouTube, discussing De La Soul's Three Feet High and Rising. He can't even recreate the beat/mix on YouTube as it would get flagged for copyright. It was unavailable for streaming/download until 2023 due to licensing issues.
My go-to example of disappearing media is the third season of Monkey Dust that ran into problems with music licensing and so it was never available on DVD and will never be screened again. (Available through nautical methods)