From moneyweek, via the Adam Smith blog, we get:
The average salary multiple over the last 37 years (1971 to 2007) is 4.54. At the 2007 average wage of £24,000, that gives an average house price of £109,000 – a fall of 40% from the peak. But if you exclude the bubble years (from 2001 to 2007), you get a 4.17 average salary multiple – which would give an average house price of £100,091, a fall of 45% from the peak.
The average weekly earnings in Australia are about $1100 per week, or $57,200 pa.
If we use the pommy multiplier of 4.17, that gives us an average house price of $240,000.
House prices only have to fall 57% to reach that level.