Not sure whether this is appropriate but having been born in Germany, I frequently check German websites for car rental, especially when local fares are high and for one way rentals. On the weekend, I booked a one way rental in NZ for early June, collecting in Nelson and returning in Queenstown. The booking is with Europcar (they wanted close to $NZ1,000 for the three days, mostly due to the one way fee), the website I have used several times brought that down to 167 Euro. This also includes excess free (!) insurance, the website is
www.billiger-mietwagen.de!
Google Translate is your friend, I guess. Friends used it in Cairns during school holidays (early April) and they paid a third of what Europcar wanted, and the booking was with Europcar. Food for thought.