TRENTON, N.J. — Democratic gubernatorial candidate Phil Murphy unveiled a potential price tag of $400 million for his promise of tuition free community college Monday, but his campaign said later he misspoke and the estimated cost could be about half that amount.

Murphy unveiled the estimate during a news conference outside Mercer County Community College, where he was joined by Democratic U.S. Sen. Cory Booker to discuss workforce development priorities. Booker has endorsed Murphy in his Nov. 7 bid to succeed Republican Gov. Chris Christie, who is term-limited.

Murphy previously said he backed tuition-free community college and views it as a pathway to strengthening the economy, but gave an estimate for the first time Monday.

He initially said the cost would be “in the area of $400 million,” but his campaign later cited a 2016 study by Campaign for Free College Tuition that estimated tuition to be about $200 million. That group bills itself as a bipartisan nonprofit organization dedicated to making tuition free in all 50 states.

Asked how his proposal differs from Christie’s stewardship of community colleges, which this year included more than $200 million in budgeted state aid, Murphy indicated it comes down to cost.

“Kids still pay,” he said. “This is making it affordable, accessible for everybody who wants to go down that path.”

Murphy’s campaign has said his proposals, which include pension funding and K-12 education aid, would result in $1.3 billion in new taxes, but it’s unclear whether the community college proposal is factored into that.

Murphy said some of the money could come from the federal government and added that the proposal would be phased in over time.

Murphy’s top competition is from Republican Lt. Gov. Kim Guadagno, who is promising to audit state government and lower property taxes.

Guadagno campaign spokesman Ricky Diaz critiqued Murphy’s community college proposal, saying taxpayers would have to foot the bill.

“By insinuating that it is ‘free’ is a slap in the face to the hardworking taxpayers in New Jersey,” Diaz said.

Murphy holds a polling and cash advantage over Guadagno, who has served for two terms as Christie’s top deputy. Christie’s job approval is at record lows, and Republicans are outnumbered by Democrats by about 800,000 registered voters.