Do you require 4k 144hz? I personally use 1080p 165hz. I have never been able to fully deduce the benefits from 4k visuals on a computer unless you sit far away from your monitor. Not to mention price.
The MSI G27C4 is a 27 inch 165hz monitor for just over 200 dollars. They arent in stock right now so if you need a backup IMMEDIATELY, go for the Acer XFA240, at 24 inches and 144hz for 200 even. Both budget, both high refresh rates, and as long as you have the tower to pair well with it (you should given you wanted 4k to begin with), you can have some of the smoothest gameplay you have ever seen.
https://youtu.be/ehvz3iN8pp4 i like to use this video as reference to my statement