$100 a year is actually not as bad as I've seen with some providers, e.g. Dropbox's 100GB account is $240/year. However, I do agree that for personal use, there are a lot of other options. Besides using a friend's place as a host, a webhost is another option if you're happy to manually encrypt and upload your data. For example, I remember Siteground use to have a 750GB storage limit before they went unlimited, so I'd imagine they'll not have an issue with a few hundred gigabytes of data, which would give you a lot more storage space for well under $100 a year
For a small business, another option is to get the boss to host the backup at its house. If the company deals with a lot of data (e.g. photography), this would work out a lot cheaper than pretty much any online backup service and assuming it's secured properly, there's no risk of a 3rd party company snooping on the data or cloud service hack or security breach (Dropbox example) exposing the backed up content. Also, carrying out a restore would be a lot easier, since the boss can take in the backed up data instead of trying to download 100GB or more off the web!