This can go in the bar, OP, please ensure you have 20 posts before posting in the classifieds, which is where you will sell your goods.
To answer your question, used parts are usually worth about half of what they are new. Some people try to ask for an items weight in gold for their stuff, used is used. However it's yours to sell so you can set your price wherever you want, just keep in mind, the closer you are to a new price the more potential buyers you will drive away. Just keep in mind you will always have low ballers too, even if your stuff is dirt cheap people will still ask for you to give it to them for free and want you to pay for shipping