Listings may be free but you pay final value fees of 10% on the end price of your listing + the postage
Ebay charge the fees to your account as soon as the item is sold and invoice once a month for payment
To check your fees go to the account tab on your MY ebay page then Summary then Fees
http://sellercentre.ebay.co.uk/private/what-fees-youll-pay
You also pay 3.4% +20p to paypal when your buyer pays that way
I usually use 15% overall as a quick rule of thumb
Read the link to fees as things like Vehicle and some other things have different fees
