PayPal – Understanding PayPal and Tracking

The costs are absolutely nothing.

By allowing PayPal to use your bank account, you are saving PayPal money - they don't have to pay your credit card company a transaction fee. That is the preferred mode of PayPal nowadays and they are doing their best to motivate people to finance their PayPal accounts with their bank accounts.

From my point of view, I'd rather use my CC and have another entity I can appeal to between PayPal and my money. But again, this means PayPal's cut from each of my transactions is lower (not that I care about it).

If you refunded the payment, rather than cancelling it, the fees are also refunded provided the payment was for goods or services.

You can partially or fully refund a buyer within 60 days of receiving their payment. Refunds are available only for transactions involving the purchase of goods and services.

When issuing a full refund, your original transaction fee is credited to you. When issuing a partial refund, a portion of the fee is credited to you.

Source: PayPal