We backed up Spotify (metadata and music files). It’s distributed in bulk torrents (~300TB). It’s the world’s first “preservation archive” for music which is fully open (meaning it can easily be mirrored by anyone with enough disk space), with 86 million music files, representing around 99.6% of listens.
You can get refurbished hard drives for around 300$/20TB (quickly searched estimation). So, 15 drives plus maybe another 5 for raid reundancy takes you back 6k$. Server to hold those drives 1-2k$ (used), UPS, internet connection and other bits’n’bobs and your total is very roughly around 8k$ (or €, as I threw the estimations on a pretty big ballpark).