Freelance Forums

I have noticed that at least several people here seem to use adsense. It made me wonder several things. First one is how many people are paying for their site, and how much it is costing them. The next one is how many people are making money off their site not including any sort of ads that someone else is paying them to put up. Next how many people, and how much money are you making off of ads on your site.

I ask all this because I am making an attempt at running my forum completely for free. I have no ads, and a friend is hosting the site, so all of that is completely foreign to me.