Speaking as a newbie - you guys got a great thing going here. The friendship, fun and knowledge are amazing. I read the posts for a week or so before I decided to join. If there had been a fee, would I have joined so quickly - no. Would I have joined eventually - probably, because of what I said before. This is a great forum. The question is - how much? Once you go with charging for membership, you incur costs to track and receive payments - driving the cost of the site up eve more. And those type of costs go up over time, hello inflated costs over time.
Charging for classifieds is an OK idea - and I would pay if I wanted to sell soemthing fishing related - the perfect target audience. Another option might be, can you get a links page that includes point and click style revenue generaton for fishing related topics such as fishing lodges, BPS etc., without incurring a (material) cost? If you had a disclaimer on the links page this might raise the necessary funds and keep the main forum ad free? Or am I still dreaming?