First of all, If you found it, it belongs to the state and not to you. Report your find to the National Museum and where you found it, they will advise the correct action to take.
It is rare coin alright have a look at
Now also there are copies of this coin, so don't go running to the bank just yet.
Values in 2003 Spinks 6494 F £450, VF £1500. This is the price you would expect to pay for such a coin if you wanted to buy it. Selling it to a dealers you would get half that. An Auction would be your best option to sell.
If you can send me a picture I would appreciate it.