If you are a commercial entity from Europe and you wish to do business in America, then at some point leading up to the settlement date of your transaction you will have to purchase USD.
Likewise, if I am a commercial entity domiciled in America and I wish to contract with any of the almost thirty (30) countries of the EU that currently use the euro as their national coin, then I will have to eventually purchase euros, will I not?
This tit-for-tat exchange of currencies is what makes a currency "dear", or "cheap".
That, and the purchasing power parity of a currency on a global basis.