Whether you need to be better about backing up your computer, or are just so excited that the PS4 is finally adding external hard drive support, you can get a 2TB Seagate Expansion external drive for $70 today, which is about as low as 2TB drives get these days.
Seagate had a spotty reputation a few years ago, but it seems like they’ve cleaned up their act; the slightly more expensive Seagate Backup Plus is the current Wirecutter recommendation, and the Expansion has a stellar Amazon review average from over 4,000 customers.