Back to the original question about damage to the engine. It is fairly certain that there will be engine damage as a result of the cam belt failing. The engine is an Interference Engine which means that when the cam belt snaps, the pistons in the engine cause damage to one or more valves (more than likely more than one!).
As others have commented as you know the car it might be worth more to repair the engine rather than buying an unknown quantity with a secondhand engine. However, it looks like the cost of repair is more than the value so time for a change. If you look at another Alfa look for one that has had the cam belt done or if not then factor it in when making an offer. I would also recommend using a specialist for cam belt changes. Good luck.