Currently, the cheapest month to rent a car at Siem Reap Airport is February. The most expensive time to rent a car is September. The cheapest prices for each month are shown above, but prices will vary based on availability, how far out you book your rental car, and of course, car type.
From Europcar you can hire a car at Siem Reap Airport from about $654 per week on average.
The length of time you can book a car hire for is subject to the inventory of the supplier. When renting a vehicle from Siem Reap Airport it should be possible to hire a car for a whole month if needed.