Do I need a visa (Australia passport)? If so, what is the process and the cost?

Kaz, did you mean that your cruise lasts for four days? How long will you stay in Shanghai? If you just transit less than 24 hours in Shanghai, you needn't apply for any type in advance. During your transit, you just need to apply for a stay permit if you plan to leave the ship to visit the city. After you get off your ship, you need to go through the immigration before you enter the city. The stay permit can be acquired at the immigration checkpoint.