I have around 10TB data stored in the cloud, including backups. Total cloud bill is around €23/month (recent price increase included).
There is a turning point somewhere after 15TB where the cloud becomes a lot more expensive than local storage, but at 10TB it’s hard to do in a reliable manner locally.
And it doesn’t really matter how you do it. If you’re the DIY type, and buy a second hand server, or a small machine, or just run out and buy the latest Synology box, you’re still paying more for storing <15TB at home in RAID. One will be more expensive in electricity, the other in purchase price.
how much data are we talking about?