I can see round trips from e.g. London for ~1000€ but to be fair business class seems to start at ~4000.

From what I can find e.g. SF to Sydney was $2300 US in 1986 (over $6000 now).

London - Sydney. Allegedly might have been as low $600 (~$2200) both ways in 1980 (though I don't think economy back then was even remotely close to modern business class...)