I used to fly slope-soaring gliders back in Auckland, and I can't recommend it enough. A slope soarer is a little indestructible foam-and-tape plane that you hurl off a mountain - the wind against the slope provides lift, and you're off. The basic kit was about NZ$300 including the radio - you had to glue it together, sand it and tape it, which no time at all compared to balsa. Aerial combat was the best. Plus, running up and down hills all day got me quite fit.