For sure. Human time costs so much more than storage.Like anything else in life, if you want someone else to do the work, it costs.
When you said "expensive" perhaps you meant some kind of service provision, rather than just the storage?
I wouldn't regard any backup approach as fit for purpose if it depended on manual intervention, unless that intervention was from a permanent team of IT professionals (and even then I'd be sceptical).Would you be comfortable with, or have the time to back up a large site on a daily basis and check which backups you should keep and for how long - especially if the backup was many 100's GB in size?
Instead, you develop and test a system (including recovery, of course), and then ensure that it runs automatically, N times per day/week, as required. (This can be really simple though, see below.) Periodic testing of backup integrity and recovery testing is... prudent.
Once the automatic system is in place, the ongoing effort to check up on it now and then is minimal.
If someone isn't personally proficient in the required areas, they can opt for a service where things are done for them by some provider (I guess XenForo Cloud falls into this category - min price for it appears to be $60/month).Buying storage can be cheap, buying a service not so cheap. If you can get it done cheaply, then don't just go for it, share it so we can all benefit.
If they are capable of doing it themselves, things can be much cheaper. Depending on your server setup, it may be possible to set up a regular backup - e.g. using rsync & mysqldump, which on Linux you can automate with a cron job. (This is what our site uses, though I didn't personally create the backup scripts. Our backups run to multiple TB.)
On any server/hosting setup on which you can't easily run your own backups, I'd very much hope that a backup option exists for a reasonable cost, or better still is included in the hosting costs. However I've never looked at any XF hosting offerings out there, other than XF's own Cloud system.
I have no idea which options you've considered, nor what kind of server you have - hence my question about which services you've considered.