Not quite true Adam.
Some insurers will now accept non standard tyres (Not the run flats they come with) so tyre prices are now greatly reduced as the choice has increased and the competition has thus reduced prices.
Motul do a gearbox oil suitable for the GTR now at around £23 a litre (And i believe a diff oil too) - so you don't have to pay £80 a litre for the Nissan supplied stuff.
Decent discs and pads can be had for around £300 a corner now. Again - the aftermarket effect.
My best friend has had one for a few years, my garage owner has one in his fleet.lol....... and he services quite a few of them too. So i do get to hear quite a few "stories" on these cars and their running costs.
Skyline on a budget [As my mate calls his) is still somewhat eye-watering mind.