This is not a hobby to try and save money on. There are park flyer airplanes on the market that are ok in a park (check your local regulations to be sure) but nitro planes are too big and usually too noisy.

As for cost, the search feature at the AMA website is your friend. This club will cost you the grand sum of $5 a year until you're 18.

http://www.jcsportfliers.org/

You'll need AMA if you don't have it already. It'll cost you $60. It's the cheapest investment you will ever make in this hobby with one of the biggest payoffs. The insurance policy alone is a steal at that price and the rest that they do on behalf of the hobby make a lot of it possible. You have been benefitting from the AMA's work from day 1. If you haven't been paying dues, now is a good time to start.