Cheapest way.

I plan to visit Buenos Aires in mid October and stay any where from 4 to 6 months. I have been inquiring abouts airline tickets. The cheapest was the less then 1 month return round trip ticktet was $ 1,400 US. the 6 month return was $4,800 US (insane). The one way ticket was more expensive then the round trip ticket, I would like a open return. In your collective wisdom what is the cheapest way.