There are others from here that have been, not just me! Namely Colin (Bok) and Vix (crystalpuma)
At a rough guess:
Channel Crossing - £65 ferry up to £120 Chunnel return
Petrol en route - £45 x 2
Petrol there - £50 (8 laps + running about)
Camping - £10+ a night
B&B - £20-£50 a night
Hotel - £25 - £lots a night (Although sharing at ringhaus makes it much cheaper*)
Ring Ticket - €140ish for 8 laps
June to August will be busiest, but the best bet for sun. Early starts are the best to get a clear track.
This site is excellent for info:
http://www.northloop.co.uk" onclick="window.open(this.href);return false;
There are lots and lots of recommended reading for a trip as you need to know what's what if your to make the most of it. This is a good guide:
http://www.northloop.co.uk/newbies.htm" onclick="window.open(this.href);return false;
* http://www.ringhaus.com/hotel_en/public/house.php" onclick="window.open(this.href);return false;
A 4 bedded room would only cost about £25 each a night based on 4 sharing. £30 each a night 2 sharing a twin. I've stayed there - it's really comfy, clean and has great food and nice beer