To reach Sao Carlos from Sao Paulo Airport:
Take the Airport Service Shuttle (price around R$ 45. One  American Dollar is about R$3,40) to the Sao Paulo Bus Station, or RODOVARIA. When you get there, walking straight ahead when you leave the escalator, they are the booths of VIAÇÃO COMETA (first one, a big one!) and just after EMPRESA CRUZ. There are busses about each 1/2 hour to Sao Carlos, the trip lasting 3.5 hours, and costing nearly R$70,00. The bus stops in the middle of the way for snack and refreshments. So take notice of your bus colour and number and do not miss it! Stop lasts 10-15min.
To reach Sao Carlos from Vircapos Airport in Campinas:
Take a Shuttle to RODOVIARIA in Campinas and from there, another bus to São Carlos - this trip takes nearly 2.5 hours.