UA, not sure about your figures to be honest as your guessing at the cost of fuel per litre.
Fuel at Newcastle is at this time is 82p per litre but only 55p at RAF Leeming and the rest of the MOD sites.
The insurance company as you well know dictate the hours required on type to fly the aircraft not the group and at this time (as it has been for the last 4 years) a PPL will need at least 5 hours on type before going solo and a further 5 hours (10 hours in total) before taking passengers which i think is quite fair and of course in our group the the last 5 hours to get up to the 10 can be flown with other group members and each halving the cost.
So by my calculations it could be quite possible to get converted onto a JP3 for circa under £4400, maybe even less if the pilot isnt in a hurry and wanted to use the airshow's (with their free fuel) as training flights.
Which ever way you look at it the JP3 at Newcastle is the cheapest Jet in the UK to buy into and the cheapest Jet in the UK to fly.
All we can say is come along one day what a flight look at the books and go from there, if you dont like it well at least know you know
Neil