Alex-
you can buy my Honda XR650L that is in Buenos Aires and ride it to Brazil via Foz do Iguazu. See my post here:
http://www.horizonsunlimited.com/hub...tina-usa-26437
If that doesnt take you there- just do a search of the forum for "jim stanley"
It's a good bike- a little ugly, but good and it has been all thru Brazil before- so it knows thet way! It is a 2-3 day ride to Iguzu from BA- not terribly interesting until you get to Brazil. But you can get your Brazilian visa processed in BA before you leave. It's really a good way to go.
Email or message me and I will give you my phone number to discuss.
-Jim