Some may recall I got a bag full of common date circulated Ike dollars at a local bank for face value. Was looking through them recently and came across a nice surprise. Had thought "wow that's an unusual color" and, sure enough, it's a silver variety. A good honest Ike that did quite a bit of time in circulation despite its rarer metal content.
I wouldn't buy it unless authenticated. Perhaps you can agree to pay the grading cost and have the seller send it away to be slabbed. If in a details holder then I think it's a very attractive example.
Buy at auction. Those tend to go for close to grey sheet, plus the buyer's fee, whereas retail list prices can be 2x or 3x wholesale. Takes more patience than "Buy It Now", and you have to be willing to walk way if you can't get your price, but over time you'll get great deals