Cheapest option for OP is to stash an off site HDD somewhere; nothing mandates that it must be in the cloud.
The advantage of Backblaze is that it's $9/month for unlimited backup of one PC (meaning desktop Windows or macOS). Unfortunately that means no Linux or NAS backup without jumping through some hoops.
IIRC, if you are geeky enough to dump all of your data onto one PC, Backblaze's cloud backup will work without paying for extra seats. They don't encourage it, but they just look the other way if you aren't overdoing it. I have no idea how strongly they police this. They have a stable business model that leverages consumer HDD storage, so they aren't at risk of going out of business.
The no-name cloud storage providers that claim "lifetime" storage for a fixed price on some StackSocial deal are scams.
Dropbox was never price competitive. Neither is iCloud+, unless you pay for the 2TB tier and spread the value with family sharing. This could be desirable for the iPhone integration and few ancillary benefits.