Hi chris,
Did the same thing on my X reg 2.0L turbo diesel.
�400 for turbo if you've lucky.
�1100 if engine affected.
The fuel system is badly designed and the fuel pump can only be recalibrated 3 times - new pump is �1000 as it times the engine management.
Parts available from Engine recon centre 01925 231333 who were the cheapest I found.
Did the engine make a whizzing sound for 500 miles or so before it blew.
If you have not driven it after it blew then it may be just the turbo - but 90% of the time its a new engine. The fuel pump can blow as well and recon �500 or �1000 new.
These Astras are very expensive if they go wrong.
Mine is fixed new engine and turbo but the engine management light stays on at first start until reved up to 4K and then OK.
Sorry for the tale of woe but it still pains me even now12 months on.
BEST OF LUCK