Well that is super awesome! Let me start off by saying I know very little about coins or grading of them. That being said I can say a little about economics. To get an idea what it would be worth just do a little research. See what graded examples are worth compared to what grading costs. As to future value, my thoughts are this. You have a coin that is presumably 2000 years old. So I would imagine the value is going to be fairly well documented and the value will also be fairly linear over time. Probably increasing at a fairly standard rate. This will be clouded a little because the value of antiquities will also be somewhat cyclic as society as a whole gets into antiques and antiquities and as that interest wanes. This interest is generally tied to what the market is doing and how much disposable income people have. Right now, the prices on antiques are fairly down so over the next handful of years you will probably see the prices increase as interest in antiques goes back up. That being said, I would guess you are unlikely to see an explosive change in value because it is so old unless a vast number somehow enter or leave the market. Just my thoughts. Sorry it isn’t more specific to your exact coin.
Mox