By Ivan BrehautRodrigo PedrosoVictoria Carlos JAVARI VALLEY, Brazil/Colombia/Peru — When teenager Isaías was offered work in the coca fields along the Javari River, he saw an opportunity to change his life. To endure the rigors of the rainforest and a heavy workload, the pay was double what he could get in the nearby towns of Santa Rosa, Islandia, Atalaia or Tabatinga — all part of the tri-border area between Peru, Colombia and Brazil in the Amazon. Isaías would be paid 500 Peruvian soles in advance, about $135, or the equivalent in Colombian pesos or Brazilian reais. At least, that was the st…