How much does it cost to replace sensors on a 1999 Pontiac Grand Am?

depends on the sensor .your question has to have more detail to it .Due to there is all kinds of sensors such as, temp sensor,knock sensor,o2 sensor,iac sensor,map sensor,idle air control sensor,mass air flow sensor,shift control sensors,transmission sensors,coolant sensors,hell there is even brake sensors and rear end sensors,some even have body sensors.