Buses for Puerto Viejo and Congo Bongo Manzanillo leave from the Terminal de Buses de San Carlos in San Jose. The bus company that drives there called Transportes Mepe and their ticket office is at the end of the terminal.
There are two towns called Puerto Viejo that you can catch a bus to from this terminal. You want Puerto Viejo de Talamanca (also known as Puerto Viejo de Limón).
There is one bus a day going at 12.00 am to Congo Bongo Manzanillo. The cost is about $12 and it will take about 5 hours (ask the driver after Puerto Viejo to stop by Congo Bongo Manzanillo) and the bus makes only one 20 minute stop in Limón for you to use the bathrooms and get something to eat or drink. When you reach Puerto Viejo you have to take a taxi to Congo-Bongo Manzanillo the cost is about $14.
MEPE bus schedule to the Caribbean:
Transportes Mepe Phone Numbers: San José:(+506) 2257-8129, Limón: (+506) 2758-1572, Puerto Viejo: (+506) 2750-0023
MEPE bus schedule from the Caribbean: