That is expensive for a ST I have a MK5 Golf GTI with business cover for all drivers and my 24 year old girlfriend on it and I pay £298 with Elephant who I got to match the online quote from Bell (same company) my renewal was almost £200 more. I am 29 with no points or accidents declared for either driver and 9 years no claims for me for 15k a year and garaged overnight.
It always pays to shop around, I would try Bell as they were the cheapest by miles however they have been increasing the costs of polices recently.