Your first consideration must be yourself , your children and family , what You can afford . If you feel Bt15,000 is stretching your financial resources too far don't agree to send so much , perhaps Bt10,000 or Bt12,000 . You must not compare Australian costs and standards of living with Thailand , people can live very comfortably on a very small monthly income . I know a young widow who has brought up and educated two children , now young adults , on Bt10,000 a month . Thailand is a lovely place for a holiday , but is not always the Utopian paradise in retirement , beware it can be a very costly honeytrap .
I write from personal experience of 15yrs , 13yrs of marriage to a beautiful woman , head teacher of a school , with a nice home rebuilt by me , another house built for her son and farmland . Thailand is Thailand and only Thai culture , customs and rules apply . It is far better to take a Thai woman to your country and stay there , where only your customs and rules apply . I don't recommend marriage other than village marriage , so partner visa is right . There are lots of menial jobs in Australia that seem well paid to a Thai , that employ unofficial staff .