As a general rule, temporary residents on 457 Visas are limited to an 80% LVR home loan so a 20% deposit plus your costs like stamp duty will be required. However, there are exceptions to this rule if you have strong employment or purchasing with an Australian citizen or permanent resident.
80% of the property value: Temporary residents on 457 working visas (and most other types of visas) can obtain a 457 visa mortgage up to 80% of the purchase price through some banks thereby requiring a 20% deposit plus purchasing costs,
90% of the property value: Temporary residents on 457, 475, 487 and 495 visas can borrow up to 90% of the property value if you are a professional with strong employment history. Generally you would be in a professional occupation with 12 months in your current job or 2 years in the same line of work. Temporary residents on 457 visas seeking a home loan above 80% LVR are also required to have part of the deposit saved.
95% of the purchase price: If the 457 visa holder is purchasing with their Australian Citizen or Permanent Resident partner or spouse (married or defacto) then some lenders will approve a home loan for temporary residents to borrow up to 95% of the property value providing they have 5% genuine savings. In this scenario the first home owners grant may be available as well as the stamp duty concessions that apply.