on avarage you should be getting 1$/month per unique returning visitor. but you need some volyme so you can sell directly to advertisers or be very lucky that your ad network can match you with buyers. if there are no good matches you'll only make 1 cent or less per user. you need 10k+ monthly users or they will not talk to you. there are other ways to make money though. instead of selling your users you can sell to your users. ask around what they need and want, then sell it to them. you do not have to produce what you are selling yorself.
That sounds astronomically high. There are sites with billions of visitors and they certainly aren't making billions of dollars. Some of the popular news sites would fit that bill and they surely have access to the highest quality and best paying ads.
