I suspect the NFL is going to play some games with the Sao Paulo ticket prices. I read that they will probably sell team allotments as part of ridiculously priced all inclusive packages to Packers and Eagle fans. And they'll sell the rest at reasonable prices to the local Brazilians, but it will require a Brazilain credit card and a Brazilian national ID # to purchase the tickets. That will effectively keep the cheap tickets out of the hands of US citizens.
I read they're pretty NFL crazy down there, so there's no concern about filling the stadium up.