David Cameron has claimed family holidays in Europe could be an average of £230 more expensive if the UK votes to leave the EU.
In a speech to airline staff, the PM said a weaker pound, coupled with increased air fares and mobile phone roaming charges, would push up costs.
The claim comes amid mounting anger from Leave campaigners about the exit warnings produced by the government.
Vote Leave accused the PM of "talking down our country".
And UKIP's Nigel Farage said the PM was trying to "turn the truth on its head".
He said rises in air passenger duty and taxes on carbon emissions were the reason for expensive holidays.
The UK's EU referendum takes place on June 23.
Speaking to Easyjet workers in Luton, Mr Cameron picked up on Monday's warning that leaving the EU could spark a recession - which was dismissed as "propaganda" by Leave campaigners.
He claimed there were "very strong retail arguments" in favour of staying in.
The PM was introduced on stage by Easyjet chief executive Carolyn McCall, who earlier told BBC Radio 4's Today programme it was "highly likely" fares would rise if the UK left the EU.
According to the government's calculations, by 2018, four people travelling together on a nine-night break to Spain could pay £225 more, with eight nights in France up £210, a fortnight in the US £620 and 10 nights in Portugal £325.
Vote Leave chief executive Matthew Elliott said Mr Cameron had not listened to warnings from Scottish First Minister Nicola Sturgeon about negative campaigning.
"It's remarkable to see the Prime Minister talking down our country and our economy day after day," he said, adding that the UK economy would grow outside the EU as a result of new trade deals with India and China.
The war of words between the two sides of the referendum debate has become increasingly bitter in recent weeks.
On Twitter, former No 10 aide Steve Hilton attacked "pathetic, patronising scares".
Mr Hilton, who is backing a vote to leave the EU, also told Today both sides were "treating people like imbeciles".
Taking questions after his speech, Mr Cameron said there were always going to be arguments within his party, which he said was "finely balanced" on the EU question.
But he said he "absolutely believed" his party could "come together afterwards and accept the result".
He rejected accusations of government scaremongering about the consequences of leaving the EU, saying he was doing the "totally responsible thing" by setting out his case.
On Sunday, the PM intervened to say the UK did have a veto after pro-Brexit Defence Minister Penny Mordaunt said the migrant crisis would hasten talks over Turkey's EU bid and the UK was powerless to stop it.
Mr Cameron rejected the idea he had been accusing Ms Mordaunt of lying, saying: "The person who made these statements got it wrong - that's life.... the record is now properly corrected."
In other referendum news, Labour's former deputy leader Harriet Harman complained that the debate so far had been dominated by men, saying broadcasters should be giving more airtime to female voices.
Ahead of a news conference on the issue, she said the most commonly-heard voices in the debate were "three white, male, Tories" - Mr Cameron, Boris Johnson and George Osborne.