Go to PayPal and click Sign Up at the top of the page.
PayPal fees are the same for both personal and business accounts. Find out more about PayPal fees.
First, contact your buyer and decide together how you will refund the money. If you used PayPal, refund the amount by going to PayPal's My Account page, then the History tab. Find the payment and click Details, then click Issue refund. Enter the refund amount, then click Continue. After you've confirmed the details, click Process refund.