If you don't feel like spending many hours in a train, you can consider travelling by plane. Especially if you have the possibility to book in advance, flying to Buenos Aires can be definitely cheap.
Which stations are served by the trains travelling from Salta to Buenos Aires?
Trains leave Salta from Salta (Salta - Argentina) and arrive at Buenos Aires (Retiro Cap.fed - Argentina).
How long to you need to get to Buenos Aires by train?
The average duration of the journey is 19 hours and 10 minutes, but the fastest connections take you to Buenos Aires in 18 hours and 50 minutes. The first train leaves from Salta at 11:12, while the last one leaves at 16:12.