It is best to assume that wallpaper does not exist in Australia. So a comparison to UK prices would be meaningless.
It isn’t something that you often see for sale, and when you do it is very expensive. It just isn’t an Australian thing.
There are a few suppliers, and one is www.wallpapersonline.com.au. Another is wallpaperaustralia.com.au who state “Wallpaper while making a comeback in Australia, has never been out of fashion in Europe”
But if those are of no help, then importing from overseas may be an option.
The USA has a Wallpaper supplier that delivers overseas, and at delivery rates that they say are “The Lowest International Shipping rates on the Internet”. Discount decorating.com, I have not used them, so am unable to say how good they are.