Things that will cost money:

• Obviously the car (£0 - £250)
• Entrance fee £20 per car
• Insurance - add as additional car to your existing insurance - £35
• Tax, pay for one month and get the rest refunded when you return - £15
• Breakdown Cover - £50
• Fuel, 2007 we did 1750 miles in a 1.1 Fiesta - £250
• Nurburgring lap £20 - £25 per person per lap
• Ferry Ticket book early get as cheap as £25 return for everyone
• Pimping out the car, up to you £10 - £100
• Toll roads (mainly in France/Swiz) - £120

In 2008 between three of us we spent £350 each on everything including food and red bull!