Car Hire Sydney to Melbourne One Way Special @ Budget Car Rental + cashback
This isnt a bad deal especially if there's a few of you and you hate the stuffing around with catching planes.
Budget have a one way deal on at the moment. Hire in Sydney - drop off in Melbourne.
If your gung-ho I guess you could get away with the trip with 4 people in the car for about $100 once you factor in fuel.
Now - just need to find three 'friends' .... :)