Venezuela's recent arms purchases are triggering an arms spending spree in South America; the Columbians purchased Kifrs from Israel, Peru and perhaps Chile have expressed interest in purchasing weapons, not necessarily fighter aircraft though. Brazil's air force is becoming obsolete anyway, 12 Mirage 2000s aren't going to cut it for a nation that size. Brazil is looking to become the leader of the continent (whether they want to share that role with Venezuela simply to indulge Venezuela' national Napoleon-complex is questionable), so they need to clearly be militarily dominant.
Rejecting the F-35 in favor of the PAK-FA is a huge mistake for Brazil. The PAK-FA might be a better plane, but the F-35 will be available in one or two years, not 6 or more (my estimate) like the PAK-FA. Most importantly, the Brazilian Navy needs replacements for its A-4s on the Sao Paulo. The F-35C with VTOL capability, could fill that role and make the Sao Paulo a viable carrier for years to come, as well as work of a smaller replacement carrier in the future. The PAK-FA can do none of that, and rejecting the F-35 will make it harder for the Brazilian Navy to get its hands on a replacement air wing.