Cable parks can be inexpensive to set up if you know what your doing. They can be set up with two towers (13M power poles can be used), one at each end, and a good motor (you can find rebuilt ones that are very strong and ideal).
And then the cable, which is a bit more pricey, concrete anchore points etc.
You can set these ones up in a 100M strip dam, some people already have a few acres and a machine....
I can't see that costing more then $5000. It'd be the insurance and liability that would cost more i think. Of coarse you could just build one and not open it to public but just use it with friends....

If perth wants a cable park, maybe start small like that and see if it all clicks then go bigger?