Air fares for last-minute trips rose by more than a fifth after Ryanair cancelled thousands of flights and Monarch went bust, new figures show.
Average prices for flights from the UK to Europe in October were 23% more expensive if booked after mid-September compared with the previous fortnight, according to travel firm Skyscanner.
Passengers travelling to some destinations saw even higher increases, such as Malaga (up 30%) and Alicante (up 27%).
Ryanair began announcing cancellations on September 15 and Monarch went into administration on Monday.
Skyscanner reported an 86% increase in demand for its website between those dates as travellers searched for alternative flights.
Ryanair's decision to cancel flights after it mismanaged pilots' annual leave affected around 700,000 passengers, while 860,000 Monarch customers held bookings with the firm when it collapsed.
A Department for Transport (DfT) spokesman said Transport Secretary Chris Grayling asked airlines to "keep their prices reasonable" to help stranded passengers after Monarch went out of business.
It emerged on Tuesday that the vast majority of Monarch customers will not receive an automatic refund, with administrators KPMG estimating that just 10%-15% of customers have bookings protected by Atol.
The scheme only covers package holidays or Monarch flight-only bookings made before December 15, meaning hundreds of thousands of people will be forced to seek refunds from their credit or debit card supplier or through travel insurance.
More than 40% of the 110,000 Monarch passengers who were abroad when the airline went bust are expected to have returned to the UK by Thursday night in the country's biggest peacetime repatriation, which began on Monday.
The operation, which is costing the UK Government around £60 million, will continue until October 15.
Civil Aviation Authority chair Dame Deirdre Hutton said: "Like any other airline, some of our aircraft have experienced delays, due to both technical faults and bad weather, resulting in frustration for some passengers.
"We're very sorry and would like to apologise to anyone who has experienced a delay.
"I can assure you that we are doing everything within our power to deliver an on-time and efficient service."