I thought about spark plug wire myself, but be aware, there are three different kinds.
The most common kind is carbon core "suppression wire" and is designed to suppress RFI by its internal resistance. I'm assuming that this would be unsuitable for your purposes.
Next would be "spiral core" wire which suppresses RFI by using a solid wire wrapped in a spiral rather than in a straight line.
The last is going to be hardest to find as I don't believe it's legal to run on public roads (may be different in Oz but I doubt it) which would just be straight up copper wire with insulation on it and no RFI suppression. Will likely be sold "for off road use only" or as "racing wire"