Seagate has introduced the Exos M series, a range of enterprise-grade mechanical hard drives available in 30TB and 32TB capacities. The two models, the 30TB CMR ST30000NM004K and the 32TB SMR ST32000NM003K, each offer a minimum of 3TB per disk and use a standard 3.
Do you know about tape backup systems for consumers? From my (brief) search it looks like tape is more economical at the scale used by a data center, but it seems very expensive and more difficult for consumers.
I used to swap tape cassettes out at a large hospital every night. If you could find some used hardware and had the technical expertise to administer it you could absolutely use tape backups. IIRC the cassettes themselves were dirt cheap, it was the big tape deck and some of the accessories that got really pricy. Probably not worth it unless it fits your specific situation.