Almost $800,000 has been spent on security guards since containers from the stricken MV Rena began washing up on Bay of Plenty beaches.
Guards have been stationed around the clock on beaches across the region since the operation began in October.
But Maritime NZ is refusing to reveal details of how the $37 million clean-up bill has been spent, for fear it could jeopardise their chances of recouping money from the ship's owners.
Information obtained under an Official Information Act request shows the cost of security, and reveals that a further $30,000 has been spent choppering food to a marae on Motiti Island to feed the response team's volunteers and staff.
Harry Hawthorn, general manager of the Rena response group, declined to detail the costs any further.
"The reconciling of total costs and breakdown of expenditure is relevant to recovery of costs from the shipowner. To make that information available in its raw data could prejudice the economic interests of New Zealand."
The costs include spending on accommodation, boats, cars, contractors, cranes, equipment and flights. Additional money went towards health and safety equipment, spill control, waste disposal and efforts to save wildlife.
Maritime New Zealand will try to recoup the $37 million from the ship's Greek owners Costamare Shipping, whose subsidiary Daina Shipping Company is due to appear in court on July 18.
Meanwhile, the Phillipines embassy has thanked New Zealand authorities for their "humane and fair" treatment of the jailed seamen.
Captain Mauro Balomaga, 44, and navigator Leonil Relon, 37, were sentenced in Tauranga District Court on Friday to seven months in jail after they were found responsible for running the ship aground on the Astrolabe Reef off Tauranga's coast on October 5. Balomaga also faced a charge of altering ship documents.
The embassy said it appreciated the "understanding and concern of the local communities during this difficult period".