If I were to sign up for a MileagePlus United Card (as United seems to have many flights to South America), I can spend $1000 through Amazon Payments and get 30K miles - however, flights require 30K going there and 30K back, and I can't afford to spend $3000 over 3 months for 50K miles - and it's not enough. Are there any other cards, airlines, or programs to get to and from Rio Airport?

I'm new to these forums, thanks so much for any help! I really need to get to Rio in late May for cheap.