"I wrote to travel agent in BKK to see about prices and they quoted 121,160THB ($4,045AUD) which really surprised me as the TA here quoted me $3,239AUD - high season and $2939AUD if I leave before 31 May. Have I misread something here as there seemed to be a lot of posts saying BKK was really cheap for OWE?? "

BKK is very good for business and 1st class tickets. For economy, the BKK price is higher than the Australia price. If youi want to pay around AUD6,500 , you can get a business class RTW ex BKK

Dave