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.
Can confirm on the 1921 Peace Dollar in MS-63. Paid $950 for one at auction and felt it was a good price. They've been tough for awhile now though ever since the 2021's came out.
I've got a Peace dollar set in the 62 to 65 range and honestly can't tell that much of a difference between them. Grading on this series seems fairly subjective.
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