You can save yourself a lot of time and heartbreak by checking out the unofficial eBay Fees Calculator before you get started. Just enter the type of auction, your planned starting bid, and what you expect the item to sell for, and hit the Calculate button. The web-based tool will give you an estimate of how much money you'll actually make after all the fees.
You can also use the calculator to do something a bit more shady. Just figure out how much money you want to make off your auction, type it in the "Desired Net Profit" box, and eBay Fees Calculator will tell you how much to overcharge for shipping.