Well, it depends on the dates you are traveling, what airport you are traveling from, if your dates are flexible and whether you are flying economy, business or first class. $800.00 is pretty fair considering other airlines are much higher.
I recently found a round-trip ticket originating from Buenos Aires going to Philadelphia with United Airlines at
www.united.com with a January 16, 2008 departure date and a January 27, 2008 return date for $1150.10, taxes, fees and surcharges included. Believe it or not, if my wife chose to travel one day sooner the cost went up to $1,629.90 and the day after costs $1,401.00 with the same airline. Normally, for me, the prices are lower when I travel from the United States and head to Buenos Aires, not always, but normally.
Do your homework, shop around and when you find the best price buy it before the sale runs out.