Paypal processing fees.

Payment of $20.00 has a $0.88 fee
Payment of $100.00 has a $3.20 fee

This is straight from Paypal...
Receiving money – Personal payments:

It's free to receive money from friends or family in the U.S. when they send the money from the PayPal website using only their PayPal balance or their bank account, or a combination of their PayPal balance and bank account.

If you receive a personal payment made from a debit card or credit card, the sender has the option to pay the fee or pass it on to you. If you don't want to pay the fee, you can choose not to accept the payment.

If the fee is passed to you, it is 2.9% plus $0.30 USD of the amount you receive. For example, if you are sent $100.00 USD by credit card, the fee would be $3.20 USD ($2.90 + $0.30).