The DroboApps for backup are called "Copy" or "Elephant Drive", if you want to research cost.
If it were me, I honestly would look into trimming that data volume down and spending less. But, if you legitimately want to protect that much data, it will cost you. If you don't want to pay, you should reconsider how important the data is.
[FlatFender]: ill put it like this, if she wasnt MY aunt, id hit on her