CATALYTIC CONVERTER STOLEN!

I've had my catalytic converter stolen!.The RAC say its been cut about a foot before the cat (coming from down from the engine). The car is old so I'm surprised the thieves took the cat.Its a 1995 E36 2 litre auto saloon  .but very low mileage. If I have to pay rather than go thru the insurance can someone give me a very rough estimate how much it will cost? Including an anti theft kit or plate to cover the new cat?..I do have protected no claims but a £250 excess and the insurance night want to write the car off anyway. There is a local garage (Bow East london) that's been recommended... going to contact them Tuesday if there not open tomorrow as it's a bank holiday..many thanks!