From Budget you can hire a car from about $718 per week on average.
Booking early can save you upwards of 23% on your car hire. Booking your vehicle at least 90 days in advance can get you a great below-average price for your desired location.
The length of time you can book a car hire for is subject to the inventory of the supplier. When renting a vehicle from Angkor it should be possible to hire a car for a whole month if needed.