Get on to tiger website and check prices and connections from either Perth or Darwin to singapore and on to Bkk or Phuket and then book a tiger domestic flight to your prefered city of departure.You do need to check several days/dates for the best prices if you have the flexibilty and I would imagine that early May would be the cheaper option as school holidays.at least in W.A.
Timing from perth is (9.30pm arrive bkk 7.50am) with a 3.5 connection wait in singapore.
Ted