Cost of living in Sydney (Australia) is 49% more expensive than in Zaragoza (Spain)
This comparison has some inconsistent or sparse data. It already provides a reliable comparison but it is not bullet-proof. It is based on 4,781 prices entered by 870 different people.
For example, you would need at least €4,309 (AU$6,768) in Sydney to maintain the same standard of living that you can have with €2,900 in Zaragoza.