If it's purely for backup, take a look at Google Cloud Storage. Pricing for Coldline Storage and Archive Storage is pretty low. - Source: Reddit / about 1 month ago
Google Drive - Access and sync your files anywhere
Azure Blob Storage - Use Azure Blob Storage to store all kinds of files. Azure hot, cool, and archive storage is reliable cloud object storage for unstructured data
Dropbox - Online Sync and File Sharing
DigitalOcean Spaces - The simplest way to cost effectively store, serve, backup, and archive a virtually infinite amount of media, content, images, and static files for your apps.
ownCloud - ownCloud is an open source project enabling businesses to host their own cloud storage while maintaining regulatory and compliance needs.
Zadara Storage - Enterprise Storage-as-a-Service Solutions (STaaS). On premises or in the cloud. Fully-managed 24/7. Pay only for what you use. Leading companies worldwide trust Zadara Data Storage. Proud to be the best cloud storage option