We are paying our subbie $52/m + GST for 1800 high 3 rail and palings butted together. That's with HWD posts and rails and softwood palings all CCA treated and averaging 40 metres/job.
There are cheaper people from Gumtree ads but I wouldn't go that way without looking at the quality, and make sure the post holes are a good depth and concreted in.
You would have to factor in things like quantity of work etc, and 18 metres won't make it a desirable job, so delivery and plant costs would need to be raised accordingly.
They would probably need to price in 2 guys for 1 day so the labour content would be high.
If you want to talk low to high, I would be suggesting the $60 to $75 GST inclusive would be a fair for a small job.
Cheers.