DMW2007,
Drop Bob D. an email or give him a call and he will answer all your questions! He responed promptly to my emails, and was very helpful and friendly when I spoke to him last year. Cost depends on which day you go in, slot times, heli type, handling required or not etc. I flew in for the first time on race day last year, with no holding and no problems, the master plan seemed to work well!
ATC were very good and even let me shoot a practice approach on the Saturday, and the radio procedures worked fine. We parked up in the Southern heliport on race day and managed to get fuel after a short delay because the bowser ran dry! The briefing was a bit over hyped on here, but I can understand why you need to attend if you have not flown into Silverstone before.
Good luck.