I believe paypal doesn't charge you anything when you send your money to your friend on a non-business issue.
https://www.paypal.com/cgi-bin/webscr?cmd=_display-receiving...
https://www.paypal.com/cgi-bin/webscr?cmd=_display-fees-outs...
Free when the money comes from PayPal balance or bank account. 2.9% + $0.30 USD when the money comes from a debit or credit card or PayPal Credit (the sender decides who pays this fee).