What is your offsite backup solution?

Right now, I have around 20TB of data in redundant ZFS mirrors, so I am somewhat protected against any single drive failing. Critical data is backed up at various cloud providers, but that's only a few gigs of all my data.

Looking at S3 pricing, It seems rather unfeasible to back up my data there or on the other "big" cloud providers, as it would cost me around $180 with AWS or half of that with backblaze.

How and where do you guys back up your data?