They are legal to own if you have a legal SBR or do not own a Uzi at all. You can sell without fear, it's the buyer who is the one who might break the law by purchasing it.
Value.. $50 or so depending on how badly someone wants one. It's a bit of a specialized item.
At the very least get it moved to a different place than the rest of your stuff as soon as you possibly can. Even better... get rid of it.