the cheapest way to travel from RJ to Salvador is by bus, but it will be a weariful travel, over 1600 km and 25 hours. The bus company is Itapemirim (R$ 199,00).
If you search for flight tickets you could find tickets to Salvador as the same price as bus tickets, but you have to search 2 months earlier. The companies are TAM, Gol and Azul. about 5 years ago