I’m assuming you mean a transferable smg? There’s no such thing to my knowledge of a legal semi OB TX Mac. They seem to take a price hit over the actual M.A.C. or RPB variants. My best guess is somewhere between $5.5k and 6.5k for a trans. smg.
Good call. Shooting an open bolt semi is not known to be a pleasant experience, so I don't think it takes a very active imagination to suppose how one ends up with a lot of wear.