that quote is huge........
its amazing the minute a garage see's an alfa badge they stick another 50% on the price. the fact is the 1.9 JTDm is the same as the SAAB and vauxhall lump and being made by fiat in on many fiats as well..
its no different internally to those engines, the differences are often with ancillary's and state of tune. as stated above Autolusso do the job for £850, alfa workshop do a similar price as do the alfa/maserati shed.
all of these guys are top draw and will get the job done quickly and properly.
get the vehicle recovered to one of the above mentioned.
BTW sorry to hear this, it's not a nice introduction to Alfa ownership, we would all say though unlike most German or Japanese marques with Italian cars in general you MUST adhere to the servicing and cam belt intervals and even adopt a policy of preventative maintenance...as a rule of thumb knock 20% of the service/belt intervals to be safe.
on this occasion whilst you are in there make sure the water pump thermostat and tensioners/idlers are replaced, I would also take the chance to remove the swirl flaps whilst you are in there and do an EGR delete and re-map.
don't know what the mileage is on your car but due to the torque JTDm engines generally tend to require clutch at around 60-85k on average...if you are unlucky flywheel too.
what I am saying is at a good specialist £2300 should do all of the above with a good bit of change...
so take this as a chance to get it all sorted and go away with a stronger and faster car.
the ducati corse with the q2 is a peach and the best 147 this side of a GTA it will be a hoot to drive when its all done.
best of luck!