A same level house extension in Australia will cost approximately $60,000 to $200,000+. Adding a room or extending your living area on the ground floor are affordable ways of creating more space.Here are some key points to consider that will help you keep your renovation costs in check.enovation costs for a same level extension are roughly between $60,000 and $200,000 depending on your situation, including material, labour and project management (ready to move in).