if you will likely stay longer than 30 days and are still in Australia consider getting a 60 day tourist visa. It's AU$60 so a bit cheaper than extending it in Thailand. Depending on where you live you will most likely need to mail your application to Canberra but I've found the turn around to be very fast (they usually send it back a day or so after they receive it). If you need more than 60 days you can get a 30 day extension when in Thailand.
It's listed as an option on their application form. I know that the Melbourne Consulate use to give these but now you need to go thru Canberra for 12 month visas (I think Sydney also does them but I haven't checked). I would suggest
Why not apply for a 12 month non imm. visa from the embassy in Canberra? You can post the application to them and they usually turn them around and post back quite quickly.
And is 24 hours but I think you need to make sure you enter the immigration section on the left after you check in. I think the rhs doesn't have a re-entry desk.