You will probably be disappointed if you don't pair it with another IPS monitor. The inexpensive monitors these days are all TN and designed for video with 1080P HD resolution and 16:9 aspect ratio. Not optimal for computer use!
I use an old 20" 1600x1200 pixel, 4:3 aspect ratio, Dell monitor (current model is 2007FP, $429). It matches quite well for pixel density with the 27" iMac. The 24" Dell U2412M is $369, 1920x1200 (16:10), and has DisplayPort (you would need a DisplayPort to mini-DisplayPort cable or adapter.)