Comptroller Tom DiNapoli estimated on Thursday a constitutional convention could cost the state at least $50 million — a figure he said was a “conservative” estimate.

Speaking with reporters at a news conference in his office, DiNapoli said the convention would have to spend money on pay for delegates and staff and their pension credits.

DiNapoli is opposed to holding one.

“Our conservative estimate based on ’67 number is $50 million,” he said, referencing the 1967 convention, the last time one was held to consider revising the state constitution. “I think it could be a lot higher than that. I’d rather see that money put to other issues. I’d rather see our attention focused on other issues.”

Voters next month will consider a constitutional convention referendum, placed on the ballot every 20 years. The referendum has been opposed by labor unions, environmental groups and other organizations who fear it could lead a stripping of key rights in the existing document.

It’s an argument DiNapoli said he’s sympathetic too.

“Normally I’m an optimist as you all know. But on this one I’m a pessimist,” he said. “I think it’s a very risky proposition to hold a constitutional convention.”

At the same time, he noted there are better means of revising the existing document now. He backs amendments also on the ballot next month that would create a land bank for development in the Adirondacks and an amendment that would strip the pensions of officials convicted of a felony/

“There’s a long list of things that are good in the constitution,” he said. “Could it be made better? Absolutely. But we should follow the current process.”