Thomas Cook customers have accused airlines of cashing in on the holiday firm's demise after being faced with high bills to book replacement flights.
People who booked flights with the company, now trying to find replacement deals, told the BBC that in some cases prices for the flights have tripled.
Fraser Mallen and his wife paid £779 in January for Thomas Cook flights to New York for next month.
But on Monday, he had to pay more than £6,000 for replacements.
The Mallens booked their US break through Expedia to celebrate the 53-year-old ex-coal miner's recovery from open heart surgery three years ago.
But after Thomas Cook's collapse, he was contacted by an Expedia representative on Monday and offered return flights to New York for two at £3,009.
However, Mr Mallen told the BBC, in the 10 minutes it took him to transfer additional funds into his bank account, he was told by Expedia that those flights had gone.
Instead, the travel company told him they could fly him and his wife out on Virgin Atlantic for £1,489 each and back on Delta for £1,570 per ticket - a total of £6,118.
Mr Mallen will be reimbursed as Expedia said it will claim the money through Atol.
But he says for others: "If you can't afford the new flight price up front until the insurance comes through, you lose your holiday."
Analysts said the prices reflected high demand on routes with few spare seats.
"People aren't sitting there rubbing their hands with glee. If sales come in rapidly on popular routes then prices go up," said John Strickland, an airline analyst at JLS Consulting.
Mr Strickland said September was a popular time for people to take holidays outside the peak school holiday period and many flights were already very full.
He said the airlines could decide to halt price increases, but said firms had to be commercially driven.
"Thomas Cook has failed because it had massive debts and it was making a loss. It's a fragile industry. More than a dozen airlines have gone bust.
"If the airlines don't make profits where they can on a minority of flights then they don't stand a chance of surviving."
How is the repatriation effort going?
Meanwhile, Dame Deirdre Hutton, chairwoman of the Civil Aviation Authority (CAA), described stage one of the repatriation of holidaymakers on Monday as "a pretty good day for a first day".
She told BBC 5 Live's Wake Up to Money: "We ran 64 flights, we brought back just under 15,000 people. That was over 90% of those we intended to bring back.
"I'm conscious that we've got a huge job to do still, because that's about 8% of the total, but a reasonable start.
"We've got 74 flights today and are hoping to bring back 16,500 people, but (have) 13 days to go and 135,000 passengers still to bring back.
"The cost split is 60% Atol and 40% non-Atol."
Dame Deirdre added that she wanted to emphasise: "Nobody is stranded, everybody will get their holiday and they will be brought back at the time they would have come back anyway."
What sort of price rises are people experiencing?
Holidaymaker Angela Mills said a flight from Glasgow to Rhodes, Greece, was £280 on Sunday, but was now £1,000.
She was due to fly from Glasgow to Rhodes on Wednesday on Thomas Cook flights. When she looked for alternatives after the travel firm's collapse, the cheapest price she could find for replacement flights for her and her husband was more than £1,000.
The company she booked her accommodation through - Jetline Holidays - eventually found her an alternative deal costing £600 extra.
But she will now have to fly from Edinburgh, and on her return spend a night in Prague before flying back from there.
Mrs Mills said she hoped to claim the additional cost of the flights from her travel insurance on her return.
What are my rights?
Anyone who has bought a future package holiday with Thomas Cook is covered by the Air Travel Organiser's Licence scheme (Atol). This means they will not be going away, but the cost of the holiday will be refunded.
However, Atol protection does not cover flight-only deals. The main alternative for travellers is to claim a refund from the provider of the credit or debit card they used, or make a claim on their travel insurance.
Kevin Spence was due to go to Florida next year in June with his family - a trip which had taken two years to plan and save up for.
But he said between checking flight prices just before Thomas Cook collapsed on Sunday and the following morning they had risen sharply.
Original flight costs of £1,800 for his family of four had now gone up to £2,500, he said.
"The cost of the holiday is now pushing up past our budget. I'm now in a position where I might need to cancel it altogether," he said.
However, Nigel Wilson said he had managed to beat the price increases by booking new flights for his holiday from Manchester to Marrakech at 12.30am BST on Monday morning.
The flights for his family of four cost him an additional £640, but he said when he checked prices later on Monday, the cost had risen to £1,500.
"If we had waited we wouldn't have had the funds to book more tickets at that price," he said.
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