I instruct in a JP syndicate at NW - see
http://www.swordsaviation.co.uk/ for information.
As an ex-Mil pilot, the reservations expressed above have some validity. IMHO there is definately something to be said for sticking to a UK/RAF type, where the engineering, instruction, operation, SOPs and Manuals etc. are readily available and (ex-)RAF. All comes down to your sense of adventure / risk...
From a PPL to something like an L-39 / Hunter / Gnat I would suggest a basic ex-Mil jet first anyway - JP / L-29.
As also stated, costs are really fuel, fuel and fuel - so long as you actually fly. However, NB you get a lot more in time wise than your average PPL machine. From NW, to ~Felixstowe, with GH on the way / back, aeros there, 3 circuits back at NW is ~40 min. Somewhere with better airspace, even less...
HTH
NoD