How can we get a Visa to China by post from Sydney? How much is the fee for single entry?

You can apply through CVASC in Sydney by post. It is suggested that you use Australia Post Express Post to deliver your application. Fee is Australian Dollar 115 for a single entry by post.
Office Address:Level 5, 299 Elizabeth Street (the Opposite of Museum Station),Sydney, NSW 2000, Australia.
You can refer to CVASC' s website for more information.