I suppose that a membership fee is always an option but think about this. As I write this, there are 498 people viewing this site (check out the home page, top right). That's 12members, 486 guests. If those guests are interested enough to look at the site, but don't want to join, what makes you think that they will come back if they've got to pay? The ad people pay based on the number of eyeballs they reach. What will happen to the ad income if the viewership drops off? If the software allows paid, ad free members that's a different story.