Whether you need to be better about backing up your computer, or are just so excited that the PS4 finally has external hard drive support, you can get a 2TB Seagate Backup Plus 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; this model is the current Wirecutter recommendation, and is has a stellar Amazon review average from over 11,000 customers.