Cheers,
I've been phoning around today and when I told the majority of companies my age they just thought I was joking around I think (especially around the 370z).
Admiral gave me a quote of £32,000 and said I had no chance insuring one at 18, he told me I'm better off sticking to a sensible car,
Another guy was saying how it's a lot more because it's a fast nissan, when the insignia has more power compared but quotes are a lot better with those.
Will take a lot of messing around online to get under 3k I think.. I tried most things on gocompare - adding my dad as the named driver and that got it down to £6300 at the lowest.
With all the comparison sites online i'm sure I'll find one that gives me a fair quote