£200 buys an excellent Dell monitor. I have two. Properly calibrated (ColorMunki Smile £75) they're more than adequate for high quality professional working.
You can spend a lot more for very marginal gains, but bearing mind the end result depends almost entirely on whatever the viewer is looking at (phone, tablet, laptop, paper print, print magazine etc) there's very little point in it. My work is regularly published at large size in print magazines, on web pages, or as big photographic prints and any shortcomings (and they're common!) are never the result of problems at my end.
Edit: the most annoying thing about most monitors is the wide-screen view. They're great for horizontal framing, but switch to a vertical shot and the image area drops to less than half. My next monitors will have a taller aspect ratio.