It is possible, as I say, that it is expensive because it is unusual. I expect you've got a few quotes for different situations using the red "insurance" tab at the top.
One issue that may be worth investigating follows from the fact that the registered keeper is not necessarily the owner of the vehicle. You might save something if you could persuade the director to register the car in your name. Whether this is feesable will depend largely on your relationship with the director. If the car is registered to you at your address, even if you didn't own it, it would be easy for you to (illegally) sell it if you fell out with the director/company.
Another option would be for the company to arrange insurance and for you to reimburse them. You should keep records of the transaction and avoid it being counted as a "taxable benefit" if doing this. Again, this would only work if there is a very good relationship between you and the company.