I have been using three of
this $200 monoprice monitor. It's listed as a 1080p monitor, but my GTX 980 and 1070 have both been able to overdrive it to 1440p and I think it even still goes to 144hz. It doesn't have Freesync or G-Sync, which is a bummer, but at $200 for a 24" monitor it's hard to complain. I bought them about two years ago now, I've been using them for at least one whole year now. I think there's one dead pixel on each of them, and one of them arrived with a loose DC power in port. My coworker and I opened it up and soldered it on (it either broke off or was never soldered in the first place...), and it works fine. The buttons on the panel are loose because we did a bad job closing the monitor up, but it works fine. I realize it's not in stock, but I believe I've seen it in stock not too long ago when I checked... though, like I said, I did order mine years ago.
I will say that no distribution of windows really scales super well into 1440p on a 24" monitor. 4K scales well because 2:1 scaling is tidy.
I agree that multiple monitors are super helpful for productivity, two should be enough for most people. I seldom do enough stuff to warrant three monitors but it does allow me to be lazier with my management of multitasking. I can leave a document open on one monitor and come back to it later, have media/video on one monitor, and my task-at-hand on my center monitor. I'll often relegate a project to one monitor, where I have a word processor/spreadsheet on one half of a monitor and a reference on the other half, and I periodically work on there while I have my 'leisure' (music/games/etc) stuff taking up my other two monitors.
Any GPU should realistically be able to drive two or three (or more) monitors, provided it has enough inputs or you're able to daisy-chain DisplayPort--which is usually a 'premium' or 'industrial' feature. That said, you won't be spanning games across multiple monitors unless you're going well above-and-beyond a game's expected requirements. For kicks I tried playing GTAV on three monitors with my 980 and I was surprised that it was playable, but the hassle of using windows on a 'super-ultrawide' "single monitor" versus having my three separate monitors for productivity wasn't worth it. If it was more convenient to switch back-and-forth I might have considered it.
