Backblaze Online Backup backs up PC and Mac desktop computers for $6/month, with "unlimited backup" for all the data attached to computer, including external USB hard drives. The personal backup product is encrypted and data in the backup is only accessible by the account owner.
The online backup service includes software to automatically manage the backups of a Mac or Windows computer. The Backblaze Online Backup software creates a mirror copy of the data on the licensed computer, except for data explicitly excluded, with a running 30 day file revision history. It cannot be used as offsite data archival or offsite storage for data that will not be retained on the licensed computer.
Read more about Personal Backup here: https://www.backblaze.com/cloud-backup.html
B2 Cloud Storage:
B2 is generic cloud storage. You can use it from any computer, any operating system or any cloud storage purpose.
Service charges for B2 are variable based on the amount of data storage, bandwidth used, and transactions performed. The baseline cost for storage is $0.005/GByte/Month (half of one penny).
Data stored in B2 product is not encrypted, making it possible to share files with other people or serve up data for websites, downloads, or applications.
B2 does not include any client software to interface with the storage. The storage is accessible via web GUI, API (with which third party software can integrate with, such as these: https://www.backblaze.com/b2/docs/integrations.html), or Command Line Tool (https://www.backblaze.com/b2/docs/quick_command_line.html)
As data in B2 is not tied to a specific computer, data archival or offsite data storage are both excellent use cases for B2.
Read more about B2 Cloud Storage here: https://www.backblaze.com/b2/cloud-storage.html