The price of the car rental depends on the car category you are booking, the duration of the booking, whether it is being made in advance or at the last minute, as well as the season and month in which you are renting the car.
Take a note that in the case of last minute bookings, since the car hire agency has to make the vehicle available at short notice, the prices in such cases are usually higher. In peak months, the demand is higher which usually fuels the daily rates.