72k pa is around $1400 each and every week.
I don't know how many aircraft C&H have or what their total utilisation is., but just as a thought experiment, say they get 40 hours per week, which means that the rental alone represents a cost of about $35 per hour.
Now add maintanence, insurance (aircraft and hangar and workshop), wages, consumeables, and and and ....
I do have sympathy for their cause, because they were there long before BAL existed.
YSBK is still supposed to be an airport and not an industrial estate.