Australia, New Zealand & the South Pacific - Underage Car Rental in Darwin

Does anyone know of anywhere in Darwin that will rent a car to someone under 25, with unlimited mileage, without paying an arm and a leg? Maybe there's an australian-specific discount code for one of the major rental companies? I'm going to be there in August and was planning to drive out to Kakadu National Park for a couple of days but have had trouble finding a reasonably priced rental car.

Try these sites-generally cheaper than hiring direct.Do have age surcharges included.Have had no problems with either but you do have to prepay.
http://www.globalcars.com.au/
http://www.driveawaybookings.com/Default.aspx
Will at least give you an idea of costs.Do read the conditions closely a lot of NT car rentals are quoted with 100km a day only.