For credit/debit card transactions above 50 USD (or equivalent in other currencies), the payment processing fee is 4.5% of the amount you wish to spend (USD, EUR, GBP, and JPY), and up to 6.5% for other currencies
For the amounts below, the fee is flat:
5.00 USD - 20.00 USD -> 2 USD
20.01 USD - 50.00 USD -> 3 USD
The payment processing fee is combined charges by the credit card issuer, automated clearinghouse network, interchange, electronic check provider, or other banking institution to process a payment.