If the revenue is the point, they need more site users, give away a hat or something in a random drawing in the forums. I'm not sure how they charge for the ads, but I would think the more people that see them, the more the site should earn. I don't think charging subscribers more money is a option at this point, and making it a membership site is going to turn off new users. I don't mind the hunting related ads, and if they keep the site free, I'm all for it.
"Let a young buck go, so he can grow."