Honestly, by using Bank Transfer.
Payment Gateways like PayPal, Visa, MasterCard and American Express usually charge a % fee for the exchange of the currency and they can’t compete with the rates offered by a Direct Bank Transfer via a Swift Payment.
If you like, you can ask as to send you a Paypal Request in EUR so you will know how much USD you are required to pay and compare it with your Bank’s exchange rate offer.