I was in the same dilemma as you. I went for the 1440p route. And it isn't true you need a 300$ GPU to support it.
I have a R9 270X that I got for 200$. I play all sorts of games, mostly league and CS:GO. But I have ran Alien Isolation and Shadow of Mordor with generally high settings. I had to take off or turn down Anti-Aliasing. But generally I just lost a few FPS. Nothing major. All games are still playable.
I think that high-medium settings at 1440p look MUCH nicer than ultra settings at 1080p. Though that is my own opinion. It's a much more inclusive experience.
Now I think I would have went the 120hz or even 144hz route if I were a hardcore FPS player. I do play CS:GO competitively (not super high rank) but works just fine. Though, if u only play FPS and you are very competitive then maybe i'd go for the 144hz route.
Otherwise, I find watching movies, working on documents/photoshop and browsing the web 200 times better at 1440p. Its amazing. I also think its more future proof given that you prob will keep a the monitor thru at least another gpu
. So For that I would go for 1440p hands down.