If you're RSOC registered, give Dominion Plan a ring. They only insure RS cars and they do very competitive limited mileage policies.
Also if you get club valuation on your car and forward them the paperwork, they will honour that as agreed value for period of the policy (needs to be updated annualy of course).
They are great company to deal with, very personal service, and the only insurance company I have ever dealt with that I would actually recomend to anyone, and I don't begrudge paying my premium to them
Fully comp on my very very modded S2 was £600 and limited mileage was £440, so if yours is in quite mild state of tune and you're not in the motor trade, it should be even cheaper.
I have speeding points and am in middle of a third party claim aswell, so if you're not, will also be cheaper