strongly recommend you at least speak to Autolusso.
AutoLusso - Quality Alfa Romeo Servicing and Repairs
They have an extremely good reputation on here. If it were me I'd have them trailer it over there ASAP.
I can dig out the bills for my JTS repair - as I recall, £2963 for post-cambelt failure repair and then a later £1000+ for a reconditioned crankshaft, also affected by the failure. Not Desira but a main dealer and representative of what you will pay. Autolusso would have replaced the entire engine with a recon unit, fitted, for £1800, with warranty.
The GT is at least more contemporary but I would also be concerned about the quality of dealership work, specifically their familiarity on type; their bread and butter is working on very recent Alfas, and the V6 hasn't been sold for a little while. I'd rather use a specialist from the off. This may go out of the window if you can claim some kind of warranty and/or get Alfa to contribute.
Again I can't speak for the V6 but this is common on the TS/JTS - cambelt life was supposed to be 60k but was reduced to 36k because they kept snapping. Frankly you've been unlucky - as you'll see, the specialist recommended interval for yours is 60k down from 72k, or four years down from I think five.
One final point: cambelt failures are usually predictable in their results; it's not a sliding scale of damage based on how fast you were going etc - it's going to have been serious, and thus cost the maximum.