Thomas Cook customers have accused airlines of cashing in on the holiday company's departure after being faced with high bills to book replacement flights.
People who booked flights with the company, which is now trying to find compensation deals, told the BBC that in some cases the prices for the flights have tripled.
Vacationer Angela Mills said that a flight from Glasgow to Rhodes, Greece, was £ 280 on Sunday, but was now £ 1
Analysts said prices reflected high demand for routes with few vacancies.
"People are not sitting there rubbing in delight. If sales come quickly on popular routes, then prices go up," said John Strickland, aviation analyst at JLS Consulting.
Mr. Strickland said that September was a popular time for people to take vacations outside the peak school holidays and many flights were already very full.
He said the airlines could decide to stop price increases, but said companies had to be commercially run.
"Thomas Cook has failed because it had huge debts and it made losses. It is a fragile industry. More than a dozen airlines have gone."
"If the airlines do not make a profit where they can a minority of flights then they have no chance of surviving."
But Ms. Mills said the increases were bad for traveler already in "a state of shock." 19659005] She was to fly from Glasgow to Rhodes on Wednesday on Thomas Cook flights. As she looked for alternatives to the travel company's collapse, the cheapest price she could find for replacement airplanes for her and her husband was more than £ 1,000. 19659005] The company she booked her home through – Jetline Holidays – eventually found her an alternative deal that cost £ 600 extra.
But she will now have to fly from Edinburgh, and when she returns she will spend a night in Prague before flying back from there.
Ms. Mills said she hoped to claim the additional cost of flights from her travel insurance when she returned.
What are my rights?
Anyone who has purchased a future package holiday with Thomas Cook is covered by the Air Travel Organizers License License (Atol). This means that they will not travel away, but the cost of the holiday will be refunded.
However, the Atol protection does not only cover flight offers. The main option for travelers is to demand reimbursement from the supplier of the credit or debit card they used, or to claim travel insurance.
What are your rights? Read more here
Kevin Spence was going to Florida with his family next June – a trip that had taken two years to plan and save.
But he said between checking air fares just before Thomas Cook collapsed on Sunday and the morning after they had risen sharply.
Original flight costs of £ 1800 for his family of four had now gone up to £ 2,500, he said.
"I am devastated.
" The cost of the holiday is now being pushed beyond our budget. I am now in a position where I may have to cancel it completely, "he said.
However, Nigel Wilson said he had managed to beat the price increases by booking new flights for his vacation from Manchester to Marrakech at 12:30 BST Monday morning.
The flights for the family of four cost him an additional £ 640, but he said that when he checked prices later on Monday, the costs had risen to £ 1,500.
"If we had waited would not have had the means to book more tickets for that price, "he said.