What Are Some Affordable Cloud Services Options for Backing Up?

Speaking personally, I'm loathed to use any of them.

A cloud is just someone else's computer and your data is then in their hands. They go under or get hacked, etc. off goes your data.

I prefer to run a SMB (Windows NT) compatible service at home and if you're paranoid and have a mate who'll help, you can always run it off site too... asking a mate is a bit like putting it in the cloud though...

Personal cloud storage (from home) is way simpler than it used to be: simple, specialized Linux distros like DietPI will allow to run a fairly comprehensive system from home. Mine deals with all my work files and runs my home music/video server too. None of this KODI rubbish ( ;0) ) and cost wise it's far cheaper than anything else. 

Free services are only there to get you to subscribe. Here's another view.

https://uk.pcmag.com/file-syncing-and-backup/3682/the-best-cloud-storage-and-file-sharing-services-for-2020

The major providers such as Dropbox, Google Drive / Cloud Storage, Microsoft OneDrive, etc are all adequate in terms of free storage, and if you have existing accounts with them for email etc, then it's already available to you.

That being said, the free storage they offer is usually only a modest amount - between 5 - 20Gb, so it depends if you want bulk backup storage for everything, or just somewhere to store a few critical files off-site as part of a 3-2-1 system. The other factor is the aggressive way their apps / desktop clients push you to upgrade. I highly recommend avoiding or removing those entirely and just stick with their web browser interface.

The lesser-known providers such as Mega do offer good free capacity and competitive pricing for large volumes in the Tb range. They also provide a personal encryption key for your account so that neither the company nor malicious intruders can access your data. (Just don't lose the key!)

As an aside to this topic, Microsoft may now be scanning your "private" files and even taking snaps of your desktop to "train" it's AI. Another reason to consider our relationship with the tech behemoths. Remember, it's not magic, it's someone else's computer that you don't control or know what they're doing with that data.