I admit this is not a helpful answer but...
If you want to have hundreds of gigabytes or more of media storage plus backups, its going to be expensive. There is no secret cheap way.
This is what makes debrid options so appealing. You can amass terabytes of media data for a cheap monthly cost.
You can then supplement that with a small nas or drive of rare or hard to find media / offline selection in which case you could probably run raid 10 with the small amount that you would actually need to backup.