I use Backblaze B2 for my backups. Storing about 2tb, comes out to about $10/mo, which is on par with Google One pricing. However, I get the benefit of controlling my data, and I use it for tons more than just photos (movies/shows etc).

If you want a cheaper solution and have somewhere else you can store off-site (e.g. family/friend’s house), you can probably use a raspberry pi to make a super cheap backup solution.