We will arrive at 00:35 at GRU and depart the next day at 20:00 so assuming we need to leave the city by 17:00 to allow transport and airport security (Sunday) we have a full day to do something in Sao Paulo that is open on Sunday. I am thinking probably the zoo.
The dilemma is since we are budget travellers the cheapest but safe way to do this.
Option 1-Stay at Fast Sleep in the terminal, about $120 for 8 hours, then leave the backpacks at a left luggage facility in the airport if they have one, take a (preferably public) bus to Tiete and a Metro to the zoo.
Option 2-Stay at a cheap airport hotel like the Ibis, we may have to get a taxi if their shuttle doesn't run at these hours which would bring the total price up, then we have to hope that Ibis would hold our backpacks while we visit the zoo and we would have to go back to get them. Plus we need to get from the Ibis to the nearest metro station which may involve another taxi if there isn't a bus.
Option 3-Stay in the city centre, find hotel near a metro for easy transport. Obviously the cost of the taxi would be more, especially that time of night. I don't think the airport hotel shuttle would be running, if it is, I think it is 35 BRL per person.
Any other options?