I don't know how much it would cost to get the window replaced, these repairs tend to vary so much from one company to the next, so if you do decide to get it repaired I would recommend shopping around.
It may be worth a call to see if it can be repaired through your insurance. Of course, excess charges, no claims bonuses and whether your future premiums would be affected are things you would need to consider.
Alternatively, if you are no longer using the vehicle, you could either scrap it (I believe the value of scrap cars it quite reasonable at the moment), or you could try and sell it for spares or repair by placing an ad in your local paper.
With regards to the stolen tax disc, be aware that even though the vehicle is taxed, failure to display could mean a fine, so don't leave it parked on the roadside.
