This varies depending on the currency and the service chosen, but there are two main charges:
The Upfront Fee
The cost you pay for the service as a percentage of your total transfer amount. This tends to be a flat fee.
Exchange Rate Margin
Most money transfer services will tweak the exchange rates in order to profit. This is a hidden mark-up using the public mid-market rate as a base. To make sure you’re not getting completely ripped off, double check the service’s exchange rate, vs the mid-market range to see what you’re being charged.
You may also pay other costs depending on how you’re paying for the transfer (e.g. credit card payments are the fastest but also the most expensive) as well as pick up options (e.g. cash pick-ups are the most expensive).