"oh please, come back when you've lived on the opal or gold...

"oh please, come back when you've lived on the opal or gold fields"

Are you now saying that we need to have cash for those transactions. If that really is what someone wanted then who are you to say they can't have it. A legal contract is by a willing buyer and a willing seller. Cash is a commodity.

Commodity

Fungible item produced to satisfy wants or needs

In economics, a commodity is an economic good, usually a resource, that specifically has full or substantial fungibility: that is, the market treats instances of the good as equivalent or nearly so with no regard to who produced them. Wikipedia