Direct buses to San Andrés (de Pisimbalá) leave every morning at 8:00 a.m. and 10:30 a.m. with Sotracauca. Cost is $5.75 (8,000 pesos) for the five-hour trip. Other buses depart throughout the day, but will drop you at El Cruce de San Andrés, about an hour's walk uphill to town. Given the questionably security of walking the road at night it is better to catch one of the morning buses.
Service to San Agustín is more frequent. Entering the terminal with your backpack you will undoubtedly be approached by someone asking, “San Agustín?” Five buses run daily via Cocnuco and Isnos ($8/12,000 pesos). The journey takes between six and eight hours.
The route is spectacular for either destination, rising through the lush foothills and crossing the high plains of the paramo. To avoid any “missing luggage” it is advised to carry your bags with you on board.
It is possible, although complicated, to travel between San Andrés de Pisimbalé and San Agustín. From San Andrés inquire about the morning “bus” to La Plata. From La Plata a jeep will take you to Pitalito. From there, regular taxis run to San Agustán. The trip will take five hours and cost about $12 (16,000 pesos). It is also possible to do the trip in the reverse direction. The cramped jeeps and narrow roads may be adventurous for some, but after all, you did come to Colombia, didn’t you?
The South American Handbook 1998 has useful information including accomodations, transport, and background information.
Lonely Planet Travel Survival Kit: Colombia is the most comprehensive English-language guide for the country.