I have a small spreadsheet where i broke it down based on reasonable expectations of cost with some padding for unknowns:
worldshoot economy business
airfare: 1800 4800
hotel: 1400 2200
food: 800 1200
car+misc: 800 1000
match fee: 600 600
ammo+ship: 500 500
totals: 5900 10300
Things get cheaper as you split room costs and others, the biggest unknown atm is how to get ammo there and the reason for the ammo cost being high are that you will lose the brass as its illegal to retain empty brass in Greece, and reloading is a no go there.
You will need to take a flight out of athens to rhodos or the ferry that is why the airfare is high, the net costs could be cheaper, but these should be decent for a ballpark. Oh, and its all in Euro, so its going to hurt a bit.