Next year is going to cost around $3150-$3500 for a team entry. Factor in tyres, brakes, fuel and fluids plus accomm (although we stay at the caravan park as usual as its way cheaper) and alcohol spending $$$ and your looking at around $5-6K for the weekend shared between 2 people.
The Event sponsors don't help you at all - except in keeping the entry fee's down to as minimal as possible. But thats not a cost saving you'll ever feel. Other sponsorship is up to you to get. If you are smart you'll do what Bris and Chris did and sign-up a co-driver that will bring sponsors with them.