Flights to "our neighbours" (São Paulo)

Hey,

I'm planning to make a trip to Argentina, Uruguay, Chile, Paraguay or Peru.
I have not been to any of these countries, so I am pretty much looking for the country with the best value. It will be a weekend-trip basically, so flight costs play a significant role here.
Does anyone know where I can compare flights going from Sao Paulo to these countries? It's okay if the website is in Portuguese.

Best,