What @[email protected] said is correct, if it's critical data, 3-2-1 is necessary. I personally use BuyVM as my offsite as it's got pretty cheap storage (~$5USD/1TB/month), but if you've got family or friends with a decent internet connection, it's trivial to set up a remote sync job to any offsite Proxmox Backup Server, perhaps on a box stored at their house.
Now, just to throw it out there, my actual 'critical data' is way smaller than my total backed up data, including my media library, random ISOs, etc. - it can be worthwhile to determine if you really need to backup everything offsite or if you can sort out some less necessary data, and only upload some data to a remote server. Maybe the answer is yes, and you'll need to account for that!
That's correct, I also pay for their cheapest VPS, which is about $3, pretty good overall for my purposes!