My PBS server has 2 datasources - one local external drive & Backblaze B2. I snapshot to the local drive frequently throughout the day & B2 once in the evening.
Yeah I don't backup any of my media zpool. It can all be replaced quite easily, not worth paying for the backup storage.
In my scenario, PBS runs on a VM on my Synology. My Synology does automated backups to Backblaze B2 daily. It averages about $5/TB for B2 storage costs for me.I only backup the critical stuff I don't want to lose.
I also wanted to back up my big honking zpool of media, but it doesn't economical to store 10+ TB offsite when the data isn't really that critical.