Dozens of airlines offer cheap paid upgrades in various forms; as mentioned the BA scheme has been axed (due to abuse). QF has never offered this, as a matter of policy (but there should be easy availability of QFF upgrades on that route). CX sometimes has paid upgrades but it would be about USD 1000 and not "a few hundred". Still a lot cheaper than the fare differential. But you would have to route NRT-HKG-SYD and the gate upgrade is only by sector. Don't believe JL ever offered it, either, for what it's worth.