The loop runs though the building, might be very easy to chop & change it to do your bit or might have been a new loop card & long run back the controls...
Again a repeater might have be very easy to chop & change it to do your bit or might have needed a card & long run back the controls...
I suspect 4k will be the cost of the works + a margin for centre, 10%, 100% who know's ?
Has the job been done on sunday night at triple the labour cost? I don't know,
If possible speak to the other units to see if they've been bum raped for 4k
I expect you'll be able to negotiate it down, however I'd assume will be using the large LPC type of co. rather than somebody small & local ?