I agree with the dudes, it's only a 50 mins flight. Try the below budget airlines. They are going for less than US$80 for roundtrip. Some even have promos going on right now for half the price.

Jetstar
AirAsia
Tiger

Do note that only Jetstar lands at the main terminal where the rest lands at the LCC terminal. I would take Jetstar to land at the main terminal for convenience since the price isn't too much of a difference.