Have just confirmed Garuda BC upgrade with ff points. 14,000 points one way. & yes Garuda do sell 1 way tickets only, from Bali to Sydney. A little under AUD$680 for economy or about $620 & 19,000 points.
I should have listened to my wife in the first place, but I didn't think we had enough points.
Thanks for the heads up, I do love this forum