The Flight Deal reports that TAM has roundtrip fares between Miami and Buenos Aires or Santiago for just $350 all-in. There are some equally good fares for travel from New York to Buenos Aires. This is valid for travel between March 1, 2013, and June 30, 2013.
Here’s a simple itinerary that’s valid:
If you keep your flights on TAM metal you can accrue United miles for the trip, so this is a great mileage run and/or vacation fare.
Do keep in mind though that both Argentina and Chile charge hefty entry fees for those entering on a US passport.
I doubt this fare will be available for long, so if you’re interested jump on it ASAP.