Thanks for all your help guys - I think I'll have to go with one of the majors due to the size of the event. Also, on occasion we'll need a heli to land in our main arena and uplift some parachutists - does this heli need to be a twin (sorry for the ignorance, I'm more of a fixed-wing type, for my sins!) as it will have to fly over large crowds to land in this arena.
Anyway, thanks again I'll contact the majors on Monday as they're up to their t*ts with Slane at the moment
Cheers