It really depends on the size and what particular features you want. If you just want a normal 20 - 24 inch monitor that is 1080p 5ms 60hz, and not worried about IPS, brightness, contrast ratios, etc...then they are pretty cheap.
A 20 - 24 inch, 5ms or less, 60 hz, 1080p, LED backlit, with built in speakers, is in the $120 - $150 range. This one is pretty good:
http://pcpartpicker.com/part/benq-monitor-gl2460hm