In South and Central America it’s often the case that flights from one country to a neighbour country may cost several times more than between the countries that are located way futher from each other. The flights Colombia-Peru, for instance, cost approximately the same of money as Mexico - Peru.
From Colombia to Brazil the tickets cost approximately $300-400. What if you want to go cheaper, what can you do? There’s one route somebody told me about. Thanks to the fact that Colombia and Brazil share the border in Amazonas, the route is this:
Colombia/Leticia –> crossing the border by land, on foot –> Brazil/Tabatinga –> Manaus