Unless you are listing the item as Good Til Cancelled, you only pay for the listing once.
In fact, you really don't have to pay even once for the Listing, if you use one of the 50 Free Auctions you are allowed each month. You could list your single item 50 times if it remained unsold.
You will pay selling fees including a fee on your shipping price and a fee for accepting a Paypal payment. This will run somewhere between 9 and 20% of the selling price, depending on what the auction closes at.
If you go for an auction, don't price your thing too low. List at the lowest price you can emotionally let it go for. Then carefully weigh and measure to make sure you cover your postage and packaging cost.
Good Luck!