Hey mate
The windy season in Brazil is from June-Dec/Jan, with August - Beginning December having some of the most consistent trade winds in the world, 20+ knots 9 out of 10 days.
All the best kite spots are in the North-East Region of Ceara. You'll need to fly to Fortaleza airport, and head North from here. There are countless spots/conditions to choose from, whether you want waves or flat water lagoons. Cumbuco is the closest spot to the airport but the lagoon gets pretty crowded these days. Generally the further North you head the less crowded and stronger the wind gets.
I couldn't tell you what the costs from Australia are, but I would imagine the flight costs would be a lot. Check out these Kite surf specific Holiday companies for info on which hotels/schools to use.
www.sportif.travel/ waveriders.co.uk/ www.planetkitesurfholidays.com/