@Beverley ******
I think as an Australian you are stuck with the 2 (possibly 3) possibilities.
1 - 800K in a Thai bank account
2 - 65K/mth coming into a Thai bank account from a foreign country
3 - combination of Thai bank account and monthly income totalling 800K
Not sure how difficult it would be to transfer from Thailand back to Australia, I'm sure there are 'horror stories', but in general I would think it's not that difficult, but that would be for you to research.
The other potential possibility, which I am told I can access as a Canadian, but which is no longer available to Australia, is to have your embassy/consulate in Thailand write you a letter of verification for your income ... after which I am told you can use that method in leu of any Thai banking requirements (I assume you need to get a new letter every year to confirm your income is still valid, but not sure as I presently use the 'money in the bank method'.)
As I said, the verification letters are no longer available from Australian (US or UK either to my knowledge) embassies/consulates, but I would check with the foreign affairs department (or whatever department is in charge of these things in Australia) to see if there are alternative ways to get a letter of this sort ... highly unlikely as it may require agreements between Aus & Thailand, or it may just be up to Thailand as to which country's 'verification letters' they will accept ... but it might be something worth while researching before you make the move.