“Re prices, yes you can buy a working 4-seater plane for £20k but it will still be a relative wreck.”
I really do not think that is true anymore. There is a PA28 – 140 in my area that has been lovingly looked after, has new ish interior (leather), a lot of engine life left and good paint that has been for sale for 12 months. No it will not be cheap to maintain as it is a c of a aircraft and quite old but it is far from a wreck. It has reasonable avionics and would be capable of light duty IFR – ideal for a first aircraft if you can afford the upkeep which the numbers above would easily cover.
Regarding 2 seaters, I fly this to Europe and Scotland etc – two up;
G-KARK
It is a superior touring machine compered to my old AA5B or DR400-160 for a PPL with no IR who does not need 4 seats, but it is way outside your price range and given your mission I would not recommend anything similar. However a 2 seat Robin might work and if you keep it on an F reg it could save you some money. I would look at your first aircraft as a stepping stone. Many student PPL’s aspire to an IR, but only about 1% of European PPL’s have one! If you go for a PA28-140 type machine and save any maintenance money left over from your pot, in 3 or 4 years you will have the money and experience to make the next step.
Good luck with the project
Rod1