Seagate’s FireCuda is one of the most popular PS4 replacement hard drives out there, mostly thanks to its built-in 8GB of flash storage that can speed up loading times, and you can get the 2TB model for just $85 today, or roughly $10 less than usual.
Even if you don’t feel like cracking open your PS4, you could pop this into an inexpensive enclosure like this one, and use it as an external drive over USB.