A typical 180hp 4 seat IFR capable spam can annual cost will be very close to;
Maintenance £5k
Insurance £2k
Parking – depends on area but London say £3.5k
Fuel £70 per hour (expect this to increase to around £130 ish over 5 years)
That is way outside your £600 a month, but a 1970’s machine in reasonable condition will cost around £35 - £45k. All you have to do is reallocate your funding. Assume your first year maintenance will be double the above if you are moving to a new engineering co.
Rod1