Paypal is only free if someone sends you funds via the friends/family option BUT its against paypal rules to use that option for accepting payments for selling a service. If you do then you risk your account being permanently limited.
So you should be accepting payments via goods/services and yes then you would pay a fee. If paypal only charged for international transactions and everything else was free they would soon go bust !! You pay paypal to process instant payments for you from buyers including from credit card funded payments.
However if you are accepting paypal for a competition then you need to read the below policy as you are risking your account being limited as you need pre-approval to use your account for something like that.