The Christchurch City Council used $3 million of ratepayers' money to purchase the Ellerslie Flower Show.
The festival was previously held in Auckland and was bought by the council in 2007 and renamed the Ellerslie International Flower Show.
However, the cost to secure the event was only made public on Thursday, following a recommendation by the Ombudsman.
The council discussed the Ombudsman's ruling in private during a meeting, before voting overwhelmingly in favour of releasing the information.
Councillors Gail Sheriff and David Cox voted against the motion.
However, Councillor Sue Wells admitted that the council probably would not have revealed the figure if it had not been instructed to.
Ms Wells says it believes the commercial sensititivities of the purchase were better kept under wraps.
She says the council is very satisfied with its purchase and is pleased the festival made the South Island city a $220,000 profit in its first year.
Ms Wells says the Ombudsman should instruct other councils to publish the price they pay for big-ticket items, to put everyone on an even footing.