It is expensive. Its easy to fit yourself and doesn't require anything special to do so.
My above "advice" was taken in jest I'm not saying use it till it stops. Ive personally never had one break and take anything else out. I've had a pully bearing on the steering pump collapse. Which meant the belt was burning itself up with friction. In the end I pulled it off. (Easy to do without removing anything and pulling the tensioner) then fitted a pair of tights over the bottom pully and alternator to get me home. Which worked.
Point is the belt shouldnt be more than £20 and given it has to come off when doing the cambelt it shouldnt be any extra. The labour should be included and you should only be paying for the part. Thats if there honest obviously.
Alfa's are no less reliable than any other car on the market. But I'm sorry the TS engine is a little bit more fragile than most. They take a bit more care than your average segment market car.
Its just a belt at the end of the day. Its cheap and easy to fit.
Alfa 166 2.0 Twinnie - LPG and a few trick performance parts