Which? has called for currency providers to offer more consistent exchange rates in order to ensure people are treated fairly.
A study by the consumer group revealed that the rates offered by some foreign exchange specialists vary considerably in different parts of the UK.
This means that a consumer who lives in a certain area and tries to purchase money from a particular company could end up paying much more than a person in a different location who is using the same firm.
While the findings relate to obtaining travel money rather than transferring funds overseas, they demonstrate the need to carry out a currency comparison in order to find the best and most competitive exchange rates.
Richard Lloyd, executive director of Which?, commented: "Currency providers need to make sure their rates are consistent to ensure a fair deal for everyone.
"While we understand that local competition may play a part in the rates set, it is unfair that people are missing out on the best currency exchange rates just because of where they live."
Mr Lloyd noted that holidays are typically expensive purchases, which means "anomalies" in exchange rates are not helpful to "hard-pressed consumers".
Which? stressed that not all high street providers are varying their rates, as some are offering identical prices across the country. However, the group's study showed that in many cases, the disparity could often be in the region of £25 – a sum it said could otherwise cover a person's taxi fare between the airport and their home.
This comes shortly after Which? criticised various banks for charging excessive fees on the "most straightforward" overseas transactions, which it said is making even basic purchases more expensive.
Mr Lloyd has called for overseas bank charges to be more clearly displayed to consumers when they open an account in order to stop them being hit with "exorbitant" charges.