Only milk, vitamins, cold weather fruits and things like sunscreen are cheaper in Oz. Most other things are expensive.
Room rent is $160 per week i should say. Might get cheaper if dump or share room. Lots of Thais there.
You could eat cheap if 2 minute noodles, not much meat, apples and bananas.
Mobile ph plans $45 a month with internet.
I would say you need $350 per week (8400 baht) minimum plus education costs plus insurance.