Pickling cars with simple management system in Python
def printCars():
    for i, car in enumerate(cars):
        print("Car #{:d}\n{{\n\tname:{:s}\n\tyear:{:s}\n\tcost:{:s}\n}}\n---\n".format(i+1, car.carName, car.year, car.cost))


cars is a global variable: that should be avoided.

Use dictionaries

    if opt == "import":
        importCars()
    elif opt == "export":
        exportCars()
    elif opt == "add":
        addNewCar()
        printSuccess()
    elif opt == "print":
        printCars()


should be a dictionary.



Also I feel like all your methods should be inside the car class as they are logically connected to it.