You may get an IR camera within $500. But if you buy a standalone IR it will be more cheaper. And another major advantage is it will be portable. You can adjust the IR as per the camera angle. So it is really better to buy a standalone IR. Always buy IR which gives a lifetime warranty with advance replacement. Which has an auto day/night setting. It is always a good idea to get the IR which will synchronize with any CCTV camera.
Read this to know more about IR
http://professionalirilluminators.wordpress.com/2013/10/10/important-benefits-of-using-an-infrared-lamp/