Copa Airlines currently has fares from New York (JFK) to Montevideo, Uruguay (MVD) for only $374 including all taxes and fees. This is a pretty amazing price, and if you have friends who want to get to Buenos Aires, it’s only a short plane or ferry ride from Montevideo.
To find dates that this fare is available, search on ITA Matrix and select “See calendar of lowest fares” around the dates you’re interested in. Once you find the fare you want, you’ll need to book it on Orbitz or another site as ITA does not handle bookings.
Thanks to The Points Guy for pointing out this deal. His site also has more detailed instructions on searching for these fares and booking them. There are a lot of available dates at the moment, but I’d hurry as a price like this cannot last.