Today there is a good fare on Copa and TAM to Buenos Aires via Panama City and Sao Paulo. While Brazil has been a bargain ticket price for the past couple months with sub-$500 fares again today from California, the discounts for Buenos Aires have been far fewer. This deal knocks about $75 off buying separate tickets LAX to Sao Paulo and Sao Paulo to Buenos Aires. Americans will need to pay $160 for both Brazil and Argentina is traveling to both countries without a current visa. You only need to pay the Argentina fee if transiting through Brazil without leaving airport.
The low fare around $700 is available for dates in August to October 2015.
Los Angeles LAX – Buenos Aires AEP (secondary airport to EZE)
$705 Copa Oct 22-29, 2015 on Priceline.com.