You're in a tough spot. You have 35 TB of files and don't want to lose any of them. As a DataHoarder, that is a valid desire.

You don't have a 3-2-1 backup system in place. If you did, no problem with your project. No need for cloud storage space.

You have a 1-0-0 non-backup system. You could lose everything you've collected in a flash. A fire, storm, quake, flood or theft and you're left with 0. Not to mention ransomware or wiper virus.

The solution? Never add files to any drive that is not fully backed up. Regularly test the backups.

Since you don't have $175 to buy more drive space, you need to delete more than half your data and dedicate the emptied drives to backups. You could even buy a SATA to USB drive dock to save money, using it with freed up internal drives.

Or you could spend $129 on a refurbished 12TB drive: https://www.amazon.com/Seagate-Exos-Internal-Drive-Enterprise/dp/B07YYKKJVZ. At least you'd protect your most important data.

There's a similar issue with self storage units. If you have stuff to fill a 26 foot U-Haul truck, you won't find a storage unit for your stuff for $50 per month. You just have to save less stuff.