Even at £300 for 256GB its steeep!
I could probably easily survive on 128GB , My OS, Apps and all the games I actually play atm only come to ~90GB. Just want the extra legroom to never need to touch anything. All my videos/photos/music gets stored on my server where mechanical drives can play to their strengths.
It's all a matter of perspective really, dropping £100 on a PSU used to be unthinkable, now it's pretty commonplace. Same with High End multi-gpu setups.
For general usage, nothing will do more for your system than an SSD. They are even a pretty decent upgrade path for old laptops and parents pc's ... just clone the old drive over onto a cheap 64GB drive (can get samsungs for under £95) and it'll run better than new.