Earlier today, Mr Key said he believed the cost would be less than that, but would still be considerable. If the council came up with a proposal the Government would likely commit funds to help out.
"The Government would make some contribution, but not necessarily massive," Mr Key said. "I don't know how much support, and the process is long and slow."
In 2010 Mr Key raised the possibility of a deal with China in which giant pandas would be lent to a New Zealand zoo, but the Christchurch earthquakes the following year put that project on the backburner.
Mr Key said Wellington Zoo had in the past been keen on the idea, but Auckland was not interested.
"Having spent a bit of time on this process I know what's involved, and it's everything from not just the panda enclosure, you actually have to have somebody who comes from China to look after them and feed them a certain sort of bamboo."
Despite those complexities and costs, Mr Key said cities such as Adelaide that had secured pandas had seen massive visitor numbers as a result.
Adding a visit to see giant pandas to Wellington's existing attractions such as Te Papa would make sense, particularly for younger visitors, he said.
"Pandas do have a remarkable attraction - you would be amazed how many people go to the cities that get them, and that's why they are fiercely sought-after."