Well flights are usually around €100, go Thursday till Tuesday, get a good spot on the camping site, either near the track or below the "party camp", definitely camp though as the craic is savage! You'll want about €500 of spending money, last year we rented a focus estate for the trip and got it for €500, you'll have to rent a car, it's a tough enough place to get to with public transport and you'll end up getting a taxi. Norways off licences are closed on Saturday afternoon so get all your beer on Thursday.
Bring the tent and sleeping bag with you as tent over there will cost around €300-400.