The topic is "Highest Denomination", therefore I would say LaSwabbie is refering to face value.
This is the highest Aussie stamp I have, issued in 1990.

There is also another $20 stamp issued in 2001, but I don't have this one.

AUD$20 is equivalent to US$14.05 at todays rate.
Images courtesy of Freestampcatalogue (I was too lazy to take pics)
Steve


