If you are travelling alone, it's the best "feel safe way" to travel between both airports (Ezeiza for international flights and Newberry for domestic flights). 

One way is A$27.15 plus tax =  A$30 total. 

If you have time to kill between both flights,  get off at the downtown stop (save your ticket stub) and check your luggage into the free storage closet.   The downtown stop is on Madero Avenue behind the Sheraton Hotel.   Arrive 15 minutes prior to departure to get your suitcases.