For trying to sell it on this site, you should list it in Classifieds. It is OK to mention here that it's listed. And it is OK to discuss what it's worth. But it is not OK to actually try to sell it in this thread or this forum.
As far as what it is worth, my guess is that $500 is too high. And you might do better to list the mica undercutter separately. That is a specialty tool that most will not have a use for. And before you try to sell it, you probably need to figure out which other machines it will bit, if any. Assuming that it actually fits your cross slide dovetail, you could start by stating the width and height of the dovetail on this machine.