For the disaster recovery scenario you’re describing, Syncthing can be a part of a backup scheme, but it’s really not intended as a standalone backup tool.
Using a backup tool opens up many more cloud storage options: https://forum.syncthing.net/t/syncing-to-cloud-blackup/21219
What’s the budget?
I’m only aware of one: https://11sync.net/
Don’t focus only on the storage space cost. There’s also ingress (upload) and egress (download) to the storage space. The cheapest storage space plans often have separate fees per megabyte/gigabyte of egress while the more expensive plans bundle generous amounts of, or free, egress.