different people from different countries, and different ads, will all have widely different costs per click. The keywords on your site, and how you get your traffic, will influence the CPC.
Based on what the advertisers are bidding for so factor that into the competition for specific keywords, niche etc But it isn't so simple to answer on here. To give you an idea, the lowest bid amount is 5 cents so you'd be looking at that range up to several dollars.