Gunner, its up to you but the Spitfire T9 out of North Wales can be contacted via Phil Winterbottom, C\O Browns Holiday Park, Towyn Road, Towyn, Conwy, North Wales LL22 9HD. The flights are generally made out of Sleap Aerodrome in Shropshire.
Lets face facts here - it aint going to be cheap. As disscussed eleswhere on pprune to operate a serious warbird in this country is expensive. Most Spit operators will arrive at a cost of around £2500 - £3000 per hour based on annual costs against number of hours flown. The owner\pilot has some 150 hrs on Spitfires now so is proberbly one of the most experianced Spit pilots around.
Can't comment on the costs quoted but I think you'll find the phrase used is 'contrabution and donation'. Best if you contact them yourself and discuss what you want to do. I believe they operate a fairly short waiting list but the last time I spoke to them they had received quite a few referals from people who had known people who had enjoyed a flight with them so cant to to bad.