Oneworld Alliance airline member LATAM has Miami MIA to Buenos Aires EZE on sale for $520 to $550 round trip for many dates from late June 2017 into April 2018.
Google Flights shows $502 fares, however, the lowest fare I found was $520 round trip. Many of the Google Flights fares re-priced at $1,000+.
These fares book in O class for Miami to South America long-haul section and B class for intra-South America flights. B and O class flights earn 100% Alaska Airlines miles.
B class earns 100% AAdvantage miles and O class earns 25% miles.
LATAM Miami MIA – Sao Paulo, Brazil GRU – Buenos Aires, Argentina EZE – Asuncion, Paraguay ASU – Sao Paulo, Brazil GRU – Miami MIA
Warning: This is a dynamic ticket pricing situation. I priced several itineraries on LATAM website that showed one price in one search, then showed no availability for same dates in next search. And some dates showed high fares over $1,000 and next search returned fares in low to mid $500s.
If you really want this $500 fare, play around with different dates.