Publico to Imbert. (Guessing every 30 minutes and 80 pesos?)
Then Caribe Tours or Javilla Tours bus to Santiago. Caribe Tours is quicker and more comfortable and the depot is nearer the center of Santiago. But if the next Caribe Tours is some time, it will have to be Javilla Tours. In this case be prepared for a toddler or a sack of beans on your lap.