Couldn't tell you if the price is reasonable as I don't know the part cost but wondered if there was a reason for the belt snap, for example frayed aux belt getting entangle etc, I've seen one or two of JTD belt snaps on the forums over the past couple of months and wonder if the JTD could have an issue that needs to be looked out for?
Sorry to hear about your failed cambelt. Please see the thread below.
I'm not sure you need the head replaced but for certain you need the help of an indi expert.
At your mileage it sends shivers down the spine if the failure has not been caused by a water pump failure. Are we going to see the cambelt replacement intervals fall in line with the petrol engines?
I have seen this thread and mentioned the fact that these engines might not bend the valves to the garage. Their response was that they couldn't guarantee the repair as they have had an experience of a customers car apprearing to be OK (no bent valves) dropping the head of a valve several hundred miles later.
Incidently the belt looked like new, they haven't fully stripped it down yet so I don't know whether it was caused by the tensioner or water pump or the belf itself.