are you sitting comfortably...
i think the last i heard it was at least 300 quid.
you'll need new keys, and probably new locks as you have no master key to copy, the keys will need to be coded and set. plus labour charges, plus the cost of getting it to the garage to do the work, probably a tow truck, or pay a lock smith to come out and unlock it, but you'll have no method of switching the alarm off, unless the lock smith lets you in and you disconnect the battery.