Cloud Backup Services
Backblaze B2
S3-compatible object storage (~$6/TB/mo). Best all-round offsite backup for a NAS.
IDrive
Cheap first-year pricing and native Synology/QNAP apps for easy NAS backup.
pCloud
Consumer cloud storage with lifetime plans; handy secondary copy.
Wasabi
Flat per-TB pricing with no egress fees (90-day minimum retention).