House prices are now plunging in more affordable suburbs of Australia’s biggest cities with the downturn contagion spreading as rate rises deter first homebuyers and Budget property tax changes turn off investors. Blacktown’s median house price has fallen by 6.7 per cent during the past three months to $1.083 million, Cotality data showed. Both suburbs are within the $1.5m cap for Sydney for first homebuyers to qualify for the Federal Government’s 5 per cent deposit scheme. Even if the Reserve Bank of Australia leaves rates on hold next Tuesday, its three hikes in February, March and May were particularly turning off dual income, first homebuyers who would traditionally be considering more affordable suburbs. Bellevue Hill in Sydney’s eastern suburbs has suffered a 6.2 per cent fall since early May in an area where the median house price of $10.975m is almost 11 times Australia’s mid-point price for a capital city house.