AUD 120,000 is only about £56k, which is a joke for someone with 10 years experience in embedded C and electronics, and all the other skills. Looking at house prices in Sydney, you couldn't buy a cardboard box for that much. Maybe banks give bigger mortgages over there, but in the UK 5x your salary is normal. A starter home in London is classed as up to £400k, and that's for an apartment.
By my estimate AUD 500,000 is about £230,000, which is reasonable for this kind of position in an expensive capital city and considering that they are advertising internationally. If they wanted a graduate who is happy to rent a box room they wouldn't have put 3 years minimum experience, hopefully 10 years.