A reentry permit is 1000 THB. A non O (not non O-A here) retirement visa is 5000 THB. The multiple entry permit is 800 THB. Do the maths as I don’t know how much you paid your initial visa…
I am Canadian, Canada and Thailand have a reciprocal fiscal agreement. Income is taxed only in the country where the pension comes from, for me, in Canada. There is no double taxation. You have to do your homework and find out if there is a similar fiscal agreement between Australia and Thailand.
In my case, they asked for a translation of my passport to Thai and an affidavit (also translated to Thai) saying that I am free to marry in Thailand. These 2 documents needed to be certified by the Thai ministry of foreign affairs. Just got my docs from the attorney (translator) who managed the MFA certification.
You get a 50 day on line on the the embassy website. Once in Thailand, you go to an immigration office (in any good size city) and you ask for a 30 day extension…