The reward was offered by Tourism Holdings, which runs the caves.
"There have been no actual takers on the reward."
He said police still had no idea who the vandals were but police believed they did not have a local connection.
"It was bad. It is still an active inquiry and we would appreciate any information," he said.
The caves were closed after the overnight attack left obscene messages on walkways and splattered white paint around the caves.
The vandals also tried to light a fire and set fire to a plastic paint bucket lid, causing soot damage to the caves' walls and ceiling.
The attack followed a fire a fortnight earlier which destroyed the ticket office, cafe, accommodation and souvenir shop at the caves' entrance.
- NZPA