Costs of building a duplex or townhouses in Sydney’s West

I am wondering if anyone has had any experience with building a duplex or townhouses in the Western suburbs of Sydney (Liverpool, Cabramatta, etc). I have so far looked at Champion Homes and Corrion Homes as potential builders, but would like to hear if there are cheaper builders out there. So far the cost estimates for a duplex including everything (site costs, appliances, landscaping, and so on) have come in around $500 k. Can anyone recommend a builder who can build a quality duplex for less?