It's very hard to find deals of $400-500. You might want to try contacting this travel agency http://www.carbone-travel.com/english.html

Depending on the season you can find discounted prices for travel to EZE, let's say if you are traveling Aerolineas or Lan Chile (if you want a cheap ticket and status miles). For AA they do have reduced fares, but it all depends when you are traveling.

Btw, they get bulk L tickets which are not upgradeable.