As far I understood if you apply for PMI your salary will be taxed in AU and the social part in Spain. So considering 3800€ Gross (basic group year 2 + block of 50/55hrs) and simulating all tax and social in Au, the NET will be around 2500€. In Spain the social/health part should be lower compared to the AU one, so I think we can consider a net of 2700/2800€ PMI 50/55 hrs (joining on the second year contract). Around 3100€ if you fly 75hrs.