Leonard Leerdam. You can get the OA visa in Aus, which means showing money in Aus bank account or super fund. The OA is valid a year. As soon as you arrive in Thailand open a bank account and start the 65k/month regime. By the time the OA needs extending you should have 12 monthly payments ready to support application for extension.
Karan Ladd. There's no fine for one day overstay. Just a stamp in your passport saying the fine has been waived. The only problem with a one-day overstay stamp is it takes up space in your passport, otherwise it means totally nothing.
Andy Gatt. If using 800k method, one letter from your bank confirming the account. If using 65k/month method you need same letter, plus twelve months of statements showing all the 12 monthly transfers.
Andy Gatt. If you meet the requirements there's nothing to pay. I've done four extensions in country, never paid a cent to an agent or an immigration officer