Cheapest I've found is 400 Aussie dollars.. Why is it so expensive?
Due to a limited number of flights and a large Brazilian expatriate population expect to book in advance by several months to get the best deal. Varig is Brazil's flag carrier, Tam is their Brazilian rival and Gol along with Ocean Air, Web Jet and BRA are Brazil's low cost carriers. Brazil's internal aviation market is deregulated so if you travel on Gol, Ocean Air, Web Jet or Azul there are cheap air fares to be had within Brazil. about 9 years ago
Try Gol airlines. Here's their route map: http://www.airlineroutemaps.com/Latin_America/Gol_Airlines_brazil.shtml
I've flown them twixt Sao Paolo and BA and it was reasonable as I recall ( it was 4 years ago). Gol are billed as the low-cost carrier airlines. Cheap but maybe not always on time!
Also look at TAM airlines & Aerolineas Argentinas. about 9 years ago