Use
http://postcalc.usps.gov/ to calculate postage. Just weigh it first so you have an idea of weight. Or EBay has like a postage calculator that a potential customer plugs in their zip code and then it calculates US postage. Check it out.
It is .60 for Delivery Confirmation and $1.90 for Signature Confirmation on top of the postage fee. Just ask for one of the two (if you want) when you go up to the counter at the Post Office. Just be sure to tack that on when you set up the shipping calculator on EBay and then indicate it in your shipping description.