All the major car-rental agencies have offices at the airport and in the larger hotels. The price you pay will depend on the size of the car, where and when you pick it up and drop it off, the length of the rental period, where and how far you drive it, whether you purchase insurance, and a host of other factors. Ask if the rate is the same for pickup Friday morning, for instance, as it is for Thursday night.
Terms change constantly.
Try to allow enough time to refuel the car yourself before returning it. The price is usually fairly competitive with local gas prices, but you don't get credit for any gas remaining in the tank.