Flights returning 110,000 passengers from overseas after Monarch's collapse will cost about £60m, according to the UK airline regulator.
More than 11,800 were flown home to the UK during Monday on 61 flights, the Civil Aviation Authority (CAA) said.
The government called it the biggest repatriation exercise in peacetime.
Monarch Airlines ceased trading early on Monday, leading to nearly 1,900 job losses and the cancellation of all its flights and holidays.
The collapse of the 50-year-old company is the largest ever for a UK airline.
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The government is set to pick up the tab for flying Monarch passengers home, but is talking to credit card companies about sharing some of the cost.
The repatriation comes as it also emerged:
- About 56,000 Monarch passengers are due to be flown back this week
- More than half are in mainland Spain or on Spanish islands, according to the CAA
- BBC business editor Simon Jack said Monarch had been looking at potential tie-ups with several interested parties before its collapse
- Those talks were partly derailed by uncertainty surrounding the future regulation of the UK aviation industry after the Brexit vote, he said
- Monarch's administrators said the airline's pension holders should see no impact from the firm's collapse
What happened to Monarch?
The UK's fifth biggest airline was placed in administration at 04:00 BST on Monday - a time when the airline had no planes in the air.
Passengers were then sent text messages informing them flights had been cancelled, but some customers were already at airports.
Monarch had employed about 2,100 people. About 250 staff have been retained to help with repatriation efforts.
Terror attacks in Tunisia and Egypt, increased competition and the weak pound have been blamed for Monarch's demise.
Advice to Monarch customers
- Customers in the UK yet to travel: Don't go to the airport, the CAA says
- Customers abroad: Everyone due to fly in the next fortnight will be brought back to the UK at no cost to them. There is no need to cut short a stay. Those with flight-only bookings after 16 October are unlikely to have Atol scheme protection, so will need to make their own arrangements
- Customers currently overseas should check monarch.caa.co.uk for confirmation of their new flight details - which will be available a minimum of 48 hours in advance of their original departure time
- All affected customers should keep checking monarch.caa.co.uk for more information
- The CAA also has a 24-hour helpline: 0300 303 2800 from the UK and Ireland and +44 1753 330330 from overseas
Who has been affected?
Alan Jee was due to get married in Gran Canaria on Saturday and arrived at Gatwick airport with 30 members of his family.
"I have spent £12,000 on my wedding and now I can't even go and get married," he said. "I am gutted, absolutely gutted, and my missus is in tears, an emotional wreck."
John Shepherd, from Tamworth, had been due to fly to Cyprus on Tuesday with his 92-year-old father.
He said they had already managed to book flights on another airline - costing a "fair bit of money", but he added: "I'm worried we've lost all the money on the flights."
What has gone wrong?
Monarch reported a loss of £291m for the year to October 2016, compared with a profit of £27m for the previous 12 months, after revenues slumped.
It had been in last-ditch talks with the CAA about renewing its licence to sell package holidays, but failed to reach a deal.
Blair Nimmo, from administrator KPMG, said its collapse was a result of "depressed prices" in the short-haul travel market, alongside increased fuel costs and handling charges as a result of a weak pound.
Monarch's owner, Greybull Capital, had been trying to sell part or all of its short-haul operation so it could focus on more profitable long-haul routes, and said it was "very sorry" it had not been able to turn around its fortunes.
What have the authorities said?
The CAA has organised 34 chartered planes from 16 different airlines - Easyjet and Qatar Airways among them - to return passengers to the UK over the next fortnight.
Chief executive Andrew Haines said passengers would not be charged for the repatriation flights, which would match Monarch's original schedule "as closely as possible", adding: "There will undoubtedly be some disruption."
Transport Secretary Chris Grayling described it as the "biggest ever peacetime repatriation".
Mr Grayling said the Department for Work and Pensions would give support to those affected and that airlines had already told him they may seek to employ Monarch staff.
Easyjet said it would be "really pleased" to hire former Monarch employees, saying it had 400 cabin crew vacancies at Gatwick Airport and 100 at Luton, as well as job openings for pilots and head office staff.
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