2002 Chrysler Sebring Gasket proplem or motor

My car was making a lot of pinging and knocking sounds and there was smoke coming from the engine area. I was also having to add water to the overflow everyday for the last 3 months. I drove it to the mechanics and he said I needed to replace the motor, I think it is a head gasket problem. My mechanic wants about $3000 to replace the motor. Should I replace the motor