I thought this would be like the backups I've heard broadcasters have of every broadcast they've ever had (I've heard of people being able to request 20 year old news clips before).
But just 50TB of data? Duplicating that would have been cheap and trivial.
I'm an independent photographer and I have my 20TB drives behind my monitor, backing up to backblaze with an offsite synology. Keeping this archive up does take time and money, but PBS should have the budget and IT deparment for this.
It depends - especially if you go back further than 20 years. The Wikipedia article for "Lost television broadcast" goes into detail:
Data requirements for this would be far, far lower than what is considered standard now.
Seriously. I'm just a random nerd and I have a home server with 96TB of raw disk space divided in to two RAIDZ1 pools which cost me around $2500 to build five years ago and has required basically zero maintenance since then.
Hard drive prices are absolutely bonkers right now but even with that in mind if I were to build a modern version of this same machine I could do it for under $10k using brand new hardware and it'd have double the storage