You should offer hybrid solutions (VPS + Storage).
Customer could select solution where VPS (512MB, 1 CPU, 20GB) + Storage (512 GB)
VPS is provided with normal backups.
Storage part mounted to /data -directory without backups.
That would provide normal system backups AND user could reinstall OS, without removing data at /data storage.
Both should be upgradeable separately. So I could keep that VPS and upgrade storage bigger.. Or vice versa. Bandwidth value should come from that side where it is bigger.