What is the prize for the major horse race held on the first Tuesday of November each year at Racecourse Melbourne?

You are referring to the Melbourne Cup, a famous horse race in Australia. According to the website of the event, "The Melbourne Cup prize money is split between the top 10 runners. The 1st takes $3,600,000, 2nd $900,000, 3rd $450,000, 4th 250,000..." etc.