Paypal offers three types of accounts: Basic, Premier and Business.
The Basic accounts do not have a fee. There are limits on monthly withdrawals and you can't accept credit cards.
Premier and business accounts carry the fee. No, it's not half of what you get; it's more like about 5%. It depends sometimes on the location; I'm in the US and noticed when I got a paypal payment from someone in Ireland or Australia, the fee was higher. Currency conversion charge, I'm sure.
I originally had a basic account, then (accidentally) upgraded because someone tried to pay with a credit card. I had to request a downgrade. You can only do this once; after that you're stuck with the premier account. So be careful.
What annoys me is that if you sell on eBay and accept paypal payments, you can't refuse to accept credit cards. This is because paypal is owned by eBay and they want to get the fees, even from one time sellers!
This gives more info on the types of accounts:
Which Paypal account is right for me?
