There are listing fees and it depends on the initial asking price, if you have more than one picture. You add a bunch of other things for a price too.... reserve price, BIN, subtitle, etc.
You automatically are charged this. If your item sells, then you are charged a final value fee, which is something like 3.25%. If you use paypal, they can also charge you 3.25% if you have a premier account (this includes your shipping fee).
The fees add up. I always calculate if it's going to be worth it to sell an item.