An investigation of airports by foreign exchange firm FairFX found that on Wednesday, some holidaymakers were being offered as little as 0.96 euro to the pound.
It also carried out research on Monday, when travellers were being offered as little as 0.88 euro.
FairFX said some providers are effectively charging holidaymakers as much as 16% commission for the convenience of buying travel money at the last minute.
Ian Strafford-Taylor, CEO of FairFX, a prepaid currency card provider, described the rates in its research as "disgraceful".
He said: "They know they've got a captive audience and once you're there, you usually have no alternative."
The value of the pound has seen some strong fluctuations since the vote to leave the EU in June and suffered a dramatic hit in last Friday's "flash crash".
Guy Anker, managing editor of consumer help website MoneySavingExpert.com, told the Press Association that where possible, holidaymakers should plan ahead when exchanging currency - as they can end up with "horrific rates" if they end up exchanging at the airport before they fly.
He highlighted travel credit cards which could help keep people's spending costs down when abroad, including the Creation Everyday card, Barclaycard Platinum and the Halifax Clarity card.
"You need a decent credit rating to get the top cards so they're not going to be for everyone," he said.
If someone ends up leaving it until the last minute, Mr Anker said they may well find they could be better off waiting until they have arrived at their destination and then taking the money they need for their holiday from an ATM overseas.
MoneySavingExpert has an online service called TravelMoneyMax.com, which helps people to find better travel money deals and avoid pitfalls.
Mr Anker said: "Airport providers that charge you horrific rates actually can provide good rates online, and if you order (your currency) online before and pick it up at the airport you will pay the online rate which is almost always a much better rate."
Mr Anker said if holidaymakers are asked when abroad if they want to pay in pounds or the local currency, they should bear in mind that if they choose pounds, the retailer will do the conversion, which can be a "terrible" deal compared with paying in the local currency.
He said: "The message for consumers is: apply for your cash in the best way you can."
There is another trick that travellers can use to try to get the best rate possible, Mr Anker suggested.
Some providers allow customers to order online and later cancel, sometimes for free and sometimes for a charge.
Mr Anker said someone could hedge their bets by making an order with a provider that allows cancellations.
If the pound improves, they could cancel the deal and then re-order the currency at a better rate, or if it weakens, they will have locked in at a time when the exchange rate was better.