I did some post PPL training and hire at WAC rather than (B)AFC, all very nice but f' expensive.
You could try Halton, just south of Aylesbury, (declaration, it's where I did my PPL and IMCR and am still a very happy member. Tail dragger and aero's also available), even without a military connection.
If you are at the north end of Buckinghamshire (a long thin county for those not familiar), Turweston is not far over the border!