There's an online pricing guide on e-bay so you just enter the weight and dimensions etc for it to give you the postage cost figure to add. Just be aware that the charges ebay impose on sellers now seems to make it difficult to make a profit on smaller stuff. There is a site called
http://www.wishnfish.com that is free to sell stuff on, give away stuff etc and people use it more for finding things locally so you wouldn't necessarily have to post anything.
[Modified by: Frazzled on December 02, 2009 04:43 PM]