I use S3 glacier on Scaleway (European cloud provider). Storing about 3TB costs me about 7€ per month including VAT. I've had to restore 1TB in the past and it cost me around 10€. Not bad for a worst case scenario. They also do mini VPSes for 3€ per month with unlimited traffic. Really nice provider, I've used them for many years.
I've only tested partial restores from Glacier since it is expensive. I've got a raidz2 array locally as insurance against having to restore from a backup.
> A 18 Tb NAS harddrive is about 320 USD. A 2 bay unifi unas2 199. It pays off in one year. Restoring data from it is free.
That single 18TB HD is hardly safe from a disaster or even plain old hardware death, and it's a single point of failure. You need at least 3 times as many HDs to start to have something you can actually rely on to keep your data for 3-5years.