Booking early is cheaper. They want to fill the seats as soon as possible. Once the seats are almost filled, then they can afford to rip some people off.
The fluctuacion depends on oil prices which determinante fuel prices for airplane. It depends also about the weather and about which class ticket we buy. Some travel agent take comision of fee so it also may be the reason of fluctuation. And if the plane has some empty spaces the prices may go up and down.
