Avianca has dropped in price of flights between Miami, Florida and Rio de Janeiro in September to $310 roundtrip. You can also find this price scattered across a few other dates on the calendar. Keep in mind that the lowest fares won't earn mileage in Lifemiles or United MileagePlus.

If you want to earn miles with United you'll want a U or T fare code, which is currently $482 roundtrip.

https://www.united.com/ual/en/us/fly...s/avianca.html

Google Flights - https://www.google.com/travel/flight...a1rP5Toe8QBXN7