That is as stupid question to ask as:
I want to buy a house, how much will it cost?
It varies depending on more detailed info. Just like a house will cost a different price in Baghdad right now then in Beverly Hills.
Tell us complete info, what type of traffic, how much foreign %, traffic source URLs, % of proxy traffic, % of hitbot traffic, location of banner, text with banners, etc, and maybe someone can give you a guess.
ZoiNk