It's an open pit lane session for 3 hours from 9am to 12, and will cost a mere £80 if you are an SIDC member and £88 if you aren't. Includes free instruction if required (ideal for fine tuning your braking and turn-in points, even if you are a regular), plus the use of the wheel and tyre van for changing wheels/tyres, storing stuff whilst you are on track.
http://shop.sidc.co.uk/prodList.asp?idCategory=72
Remember, this is the same day as the Time Attack/Drifting series, so it's going to be a great day out. If you are just coming along to watch/take photos etc, if you are there before about 10:30am, then you most likely won't need to pay to watch the TimeAttack competition and Drifting in the afternoon & early evening
John