just buy a new screen as it sometimes counts as a claim on your insurance 
+1
my mate got his windscreen replaced and the insurance company said he would still get his ncb, however when renewing he found out the ncb was only valid if they stayed with that company...
try see if any friends know a friendly window replacer, my cousin does, im onto my 4th windscreen (place I work has loads of lorries and loads of debris on the road) and each time its only cost me around £15 more than my winscreen excess