Bring ear plugs. In South America they love to play cheesy 80s movies, like Death Wish or Jean Claude Van Damme at the maximum possible volume.

try to stay a few days in mendoza, a lot of thigs to do and you can rest as by bus is aroud a 22 hours trip

Take a bus from Santiago to Mendoza and then take a bus in Pesos from Mendoza to BA, it be cheapper. There are lot of services and very good ones, pick up a "suite" bus with 180 degree seat...good luck

There are tons of cheap bus options to go from BA to SCL. The twenty four-thirty hour trip is easy (make sure you pick a good bus--ask for pictures of your seats before you buy them) and the scenery is awesome.

There is a lot of possibilities depending on what do you want to see and also how much time you will going to spend, from Santiago Bus Terminal its easier to get many Bus companies like Turbus that cross the border to Argentina,from Santiago it takes about 8hrs to get to Mendoza, in the way you may have the chance to see the Aconcagua (Biggest Peak of Southamerica) you can stay there is cheap and safe, where its a marvelous option going to Las Leñas, plus try some wines (most of the best wineries are from the region). From Mendoza to Bs As its easy too from daytime buses to midnight so, i recommend you to take a few days before arriving BsAs, also there is the possibility to take the train but not sure of its schedules. Look for Andesmar, and el rapido companies for direct routes.

I studied in Cordoba, Argentina in 1999. I took a bus trip to BA with my host sister and it took 24 hours. It is really long, but it is worth it because you really get to know the locals and local cultural. BA is an amazing city and the city to visit. I would agree with Mariano when he says to take a flight to Cordoba and then go by bus. It would take too long from Santiago to BA. Hope you have a wonderful time. Argentina is one of the most beautiful countries on earth with the friendliest people and AMAZING food. :)

You may want to choose a flight from Santiago to Cordoba and then a bus from Cordoba to Buenos Aires. The flight is 1:30 hs and the bus will take 7 hs. There are very good buses companies departing from Cordoba. Good Luck!

I did this as a bus-plane combo. At the time it was cheaper to take the bus over the Andes to Mendoza, then catch a flight to BsAs than flying straight from Santiago. It was maybe 7 hrs from Santiago to Mendoza. You could then take an overnight bus from there to Buenos Aires. I think that was another 12-13hrs.