Couple of points need clearing up here.
£500 examiners fee for an IR renewal is complete nonsense. £150 is more usual plus in a single about 1 hour flight time (usually less).
Training in ones own aircraft is allowed for the IR now. No reason to expect this will change. The main requirements are that the aircraft requires approval from the CAA in particular the provision of screens and appropriate equipment. The cost of this will be much less than the savings from operating your own aircraft.