Bike insurance for a new driver... How much? (UK)

When I reach 17 I am wanting to be able to have a motorbike liscence, and this of course means insurance.
Could anyone tell me of any places who might give a quote, even though I am not likely to buy for another few years... or atleast give me a rough guesstimate of how much it might cost.
The bike would be worth about
Could anyone tell me of any places who might give a quote, even though I am not likely to buy for another few years... or atleast give me a rough guesstimate of how much it might cost.
The bike would be worth about