Fairfax Corporation, Two coins from 1781 and 1784, New South Wales ca. 1925, nla.obj-157659805
Estimating the current value of historical monetary amounts is not a straightforward process. It is harder to get an accurate and meaningful comparison the further back in time you go. There are some good websites that will give a calculation, but they can provide quite a variation on the figures they produce.
For monetary values dating back to the 19th century it is important to note that there was no "Australian" pound at that time. The rate was fixed to the British pound, and there was no national Australian currency until 1910. For a good general guide to the old Australian currency try the Wikipedia article which describes the issuing of notes by private banks and the use of British coinage.
For currency converter websites you could try the Current Value of Old Money website. It lists a variety of online resources, including "How Much is That?", which in turn gives links to various calculators. You can convert figures according to average earnings, GDP, retail price index and more. Each calculation method produces widely varying results.
The Reserve Bank of Australia also has an inflation calculator which is easy to use and calculates the change in the value of Australian currency.
A website which goes into more detail on the issue is Measuring Worth. It contains several calculators, and an explanatory essay on the complexities of measuring worth.
The ABS article titled Prices in Australia at the beginning and end of the Twentieth Century was published as a feature article in the 2001 ABS Year Book.
