$0 for this one
Dont register company names. Commonwealth is one if the biggest banks in Aus and NZ, and they operate in Asia, US and the UK.
The .com probably sold to a new domainer thinking he could sell it to the bank. It sold in 2008 and 12 years later its still sitting there not used or sold. The bank could take it through the courts if they really wanted it.
The bank uses the .com.au because they're an Aussie bank.