BackBlaze used to be the cheapest for unlimited storage last time I looked https://www.backblaze.com/cloud-backup.html
We use Crash Plan Pro as a cloud backup for my business, however before that I have used tapes for many years, bought an LTO-2 tape library cheap and store the tapes offsite.
https://en.wikipedia.org/wiki/Linear_Tape-Open
As you can see I'm using a really old version but 200 GB per tape is no biggie when you have a library that swaps tapes for you during backup. If buying a single drive I would advise bigger capacity.
We use Crash Plan Pro as a cloud backup for my business, however before that I have used tapes for many years, bought an LTO-2 tape library cheap and store the tapes offsite.
https://en.wikipedia.org/wiki/Linear_Tape-Open
As you can see I'm using a really old version but 200 GB per tape is no biggie when you have a library that swaps tapes for you during backup. If buying a single drive I would advise bigger capacity.