It's really unclear to me if domestic fares will come back down to "normal" between the WC and the Olympics, so it is a bit tricky to do the calculations right now. Domrstic fares are usually the lowest if purchased well ahead, though.
Domestic carriers include TAM, GzoL, Azul, and Avianca Brazil, so check those flights on their sites. Also try to get an idea of where the MAO and IGU flights route through; flights most probably will not be direct.