It will work on a Sony Alpha. And can be useful when you do travelling. I suggest you keep it. You can probably get a lot less than $200 for this lens if you sell it. Not worth it. Keep it and use it. But before you use it, make sure you check that the lens and camera are both free from fungus.
BTW the full description of your lens is this:
SIGMA 28-200MM, F3.8-5.6UC ASPHERICAL (Sony/Minolta Mount).