Standardization [1] for backups. A tape with 2.5 TB (uncompressed) goes for 30 EUR. The LTO-6 (affordable current iteration) drive itself goes for 300-500 EUR if you buy it second hand. Cheaper if you grab one without casing and FC, but you'd need a FC switch and a FC HBA. I went for a SAS HBA instead, although since I already for fiber through the whole house, FC would've been suffice.

[1] https://github.com/LinearTapeFileSystem/ltfs