Regional flights in South America are ridiculously expensive.
Especially when compared to South East Asia, where I come from.
Thus, I had to look for an alternative way to get from Colombia to the north of Brazil, where I intend to cross the border into Venezuela.
Thankfully, I found out that Colombia and Brazil are connected by 2 neighbouring towns located in the Amazonas: Leticia and Tabatinga.
The cheaper alternative to get from Colombia to Brazil (and vice versa) is to take a domestic flight, cross the border, then fly (or cruise/ride) in Brazil. Here is a quick guide.