Hello there, welcome to Bitcointalk.
I would start by posting a sales thread in
Collectibles forum with your desired asking price. You can also auction the coin in the same forum if you prefer that.
Use a trusted escrow like minerjones and you will be safe. Do not deal without an escrow.
You can prove legitimacy of the item by 1) posting a picture of both the front and the back of the coin with your forum username and current date, and 2) when the sale finalizes, send item to the escrow to verify the legitimacy and condition of the item. Escrow can then ship item to the buyer after verifying the item is as described. This is important for both yours and buyer's safety.
As for the price, I don't realistically see it going above 1.05-1.10 BTC given the current price of Bitcoin and even that might be generous, but you never know, you might find someone looking for 2011 Cas and willing to pay a premium for that but I highly doubt that.
Best of luck with your sales.