Just make sure that you are happy with the mounting piece with whatever you purchase as I find that is the main thing that annoys the hell out of me. Some of them dont have anything you can use to mount onto the top of a monitor. Most webcams are much of a muchness, so I wouldnt spend a huge amount. I would say under 100 will get you a decent one for sure. Keep in mind it is a webcam, therefore you dont need super quality because it gets cut down anyway when used with skype etc.
One with a decent microphone inbuilt is also a big win!