Rental cars are an excellent choice for a longer period. Cost saving is mainly, due to fuel (rented vehicles are practically new, and therefore their consumption is lower), insurance of cars and persons (costs are taken over by the company that handles your vehicle).
Savvy travelers favor air travel because it's faster and less a accident prone than other methods of travel. Air travels can reach most domestic destinations in hours; international travel seldom takes more than 24 hours.
