The can pictured is the old, traditional two-stage style that you see in movies and typically associated with that gun. It almost synonymous with MAC-10. I'd say $200 is fair as long as you know you a buying it largely for looks. There are new cans that are much more effective, much easier to maintain, much smaller, and much easier and appropriate to use on other barrels of what is usually a fairly small gun given the caliber. There is a fairly good chance the can may be on the end of it's lifespan. Look at it this way, the seller is simply recouping his transfer tax, so the can to him is basically worthless. If it was any other accessory, many of these older systems would really be considered disposable if it wasn't for the paperwork and cost. A good quality modern can will last indefinately. If funds permit, I would buy it, clean it up a bit, and not shoot it, and get a separate modern suppressor that you can use for various guns. Some might say why not just buy a fake suppressor, but that's another issue.
BTW, in moving from a socialist state to a free state, I did pretty much what I suggested above, but I did have some extra cash at the time.