Philanthropist Gareth Morgan has pledged to stump up the difference to buy a beach in the Abel Tasman National Park.
A crowdfunding campaign to raise $2 million to buy the land at Awaroa and secure public access has received pledges of about $1.4m.
In a blog post, Mr Morgan said he would buy the beach for his family and allow the public similar access to what they had now.
Mr Morgan said public money should not be spent on the beach as it was not a wise use of resources.
"But it doesn't follow at all that this project is an appropriate way to spend public money. Before any politician commits taxpayers' money to any project they should think beyond the kudos of the publicity and be sure it is the most beneficial - and hence responsible - way to spend the next million of other people's (ie taxpayers') money."
When his family have finished enjoying it, he will give the land to the Department of Conservation.
But the man behind the campaign, Duane Major, said Mr Morgan's offer was a "distant plan C".
Mr Major said Plan A was to raise the money with people power, and Plan B would be relying on a top-up from the government or a rich benefactor.
"I don't want to diss him, it's better than some other dude getting it. If New Zealand says, no, we don't want it, well, I'd rather have him than someone else. But there would be a bit of sadness there if we weren't able to pull it off," he said.
He said Mr Morgan's comments were more about making a political statement about where public money should go.