Mexicana fare QLABUE, 2-day minimum stay. Non-refundable coach.
Best way to find availability is to go to matrix.itasoftware.com and choose month-long search, from JFK (or enter LAX) and destination EZE. That will pull up a calendar showing the departure dates with the $287 fare available. Only available a few days in August, for instance, but every day in November. Last day of travel under this fare is December 9.
This amounts to $59 each way plus taxes and fees.