Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Eugene to Argentina as you normally would.
In terms of precipitation, rainfall in Argentina ranges from 2.0 - 3.9 inches per month. January is typically the wettest month, when rainfall can reach 3.9 in. June is typically the driest time to visit Argentina when rainfall is around 2.0 in.
If weather is an important factor for your trip to Argentina, use this chart to help with planning. For those seeking warmer temperatures, January is the ideal time of year to visit, when temperatures reach an average of 77.0 F. Travelers looking to avoid the cold should look outside of June, when temperatures are typically at their lowest (around 51.8 F).