Actually, AMA will only cost you $1.00 until you turn 19($15 if you include "Model Aviation" magazine). I can't say much about the dues at the local club, but I haven't heard of dues being $200 in any club. Many clubs even have reduced rates for juniors and some also give you a break on your first year (to encourage new pilots to join). So money should not be a problem. Of course, if you hit someone with a nitro plane in a public park, AMA's insurance will not cover you because that would be considered gross negligence, especially now that numerous people have pointed out the dangers of doing so. (any decent lawyer will hit you with the same thing when they sue your parents).
Someone else pointed out that there are small electric planes that are designed for park flying. You should stick to those in the park. If you can't follow a few simple rules, you should not fly at all. I certainly hope you don't carry your disregard for safety into the cockpit of your full scale.