I use a chromecast and it's the best thing you can get for $35, get the first gen and it's $20 (not that much of a difference anyways)
As someone mentioned, you can cast your desktop on it as well
there's a setting in most games saying which monitor to select.
Other option would be, if you're not using the other two in game, turn them off before launching the game, yes it's a hassle but doesn't take more than a minute
Do you mind listing what you paid and then comparing that to what you could've paid for them if you waited till tomorrow?
[color=teal]No idea about the M.2 but the Samsung Evo 850 480GB is on sale for $179 (and there's a $20 discount if you use visacheckout if you spend $200) at newegg...