I hope S3 will stay the same and get cheaper each years. It is meant to be the foundation. That's why you have Dropbox built on top of it.
I personally use Delimiter's Obj.Space service. I bought a 2tb bundle, with 20tb of monthly bandwidth, for 3 years. It was a one-time fee of $100.
I know OVH has some attractive offers too.
https://www.delimiter.com/objspace-object-storage/ https://www.ovh.com/us/cloud/storage/object-storage.xml