How do i get cheap airline tickets?

I want to travel to argentina this summer, tickets are typically 1500 bucks return for a 1 month visit. Does anyone know any way to get this cheaper, i have 10 days in which I can leave and 10 days leeway on when I can return, is there a list I can get on and if someone cancels at the last minute they call me to take their place? I will be travelling from Vancouver to buenos aires, any help would be appreciated