So its a crack rather than a chip? How bigs the crack?
Most insurance companies will get AutoGlass to come out and repair it for free if its repairable. If you want to replace the windscreen you usually have to pay an excess of around £65-£70 which wont affect your NCB.
If they dont cover it (id be surprised if they dont), then to give you a rough idea VW wanted £300 odd quid (I think, it was a while ago now) to replace the windscreen on my MK5. Bare in mind mine has light and rain sensors so will probs cost a little more than it would to replace one on MK3.