ferry or tunnel - £70 to £100ish.
Petrol - however much to dover, plus 300 miles the otherside to Nurburg. each lap is 14miles at a much lower MPG that you would expect. I did a tank in the M5 on 10 laps, so that would be about £80 worth.
accomodation - B&B is about 40 euros a night I think. someone will correct.
beer and food - we spend almost everynight at pistenklaus and probably spend about £30 to £40 a night on steak and good few beers.
I probably hold the record for managing to spend about £5-6k on one trip, but most of that was repairs to a Golf diesel and a small part of the track! something to bear in mind though. Even if your car is cheap, a small accident at the ring will be £1000+ bill from the track itself.