In all seriousness most people don't have that much data to backup. But I can see it might be possible, but it isn't going to be necesarrily cheap. Assuming that this data is a positively must KEEP, then using the 3-2-1 rule of backup here is what I would suggest.
1. Need to have a second synced copy. So you are going to have to purchase some kind of NAS or large storage device. You can go your own DIY route (FreeNAS) or BackBlaze storage Pod 3.0, or something like Drobo. Plenty of lower cost options out there. But it will cost some money to do it.
2. Use BackBlaze or CrashPlan for an offsite replication. There are no limits! I use BackBlaze for mine and have about 2 TB backed up there. It took about a week to get it all there because there are upload limitations by your ISP and by them, but it will eventually get it all. For $60 a year, you can't beat it!
3. Writable media (Blue-ray or DVD) is a viable option, as it is cheap but complicates recovery. And it has longevity issues. It should not be thrown out if keeping cost low is a priority. Also if the data is so rarely used, then this would be a better solution than paying for the energy and cost of hard drives.
1. Like any filing system, physical or digital it needs to be checked, purged and arranged on some kind of annual or semi-annual schedule. To get rid of stuff no longer needed, and to make sure you do not have duplicates, and to see if you are going to need more space this year. I simply have an internal 4TB drive that I use to sync data, a second drive for image backups of the computer, then I use backblaze for offsite storage. I know, I have 4 copies, but it makes me feel safe.
2. It seems like priorities haven't been established when it comes to retrieval. At times it appears Cost is your highest priority, then at others convenience. You won't be able to have an extremely convenient cheap solution. You need to decide which is the highest priority, and then the next and then the next.