Well I don't know that much about Athenian vs Roman navy but my 1 impression was that Athenian and most Greek states were crewed by free men while the Romans used slaves. That might be a wrong impression but it would change the cost of labor I'd guess.

Also sailor was a respected occupation among Greeks- not as much among Romans. Though if all the factions share ship types it wouldn't make sense to have different costs anyway.

I've read that typical wages for a middle class Hoplite were 40 drachmas a month? And its roughly 6,000 drachmas per talent? So 1 talent would pay 150 men for a month. So if a single trireme cost 2 talents and we figure a ship/fleet represents 10 ships then 20 talents to build- another 1 talent for repairs per ship over 6 months and crew of 200 per ship upkeep would be 90 talents for 6 months.

Since we can't disband the crew when ship not in use in the game I figure half that is fair since in a 6 month period of the ship in service it might actually only be at sea for 3 months. Depending on conversion to game currencies then roughly that could be 1,000 build cost and 2,250 upkeep for a single "fleet" of tiremes. Seems a bit much unless the economy is radically altered so maybe half that? 500 build cost and 1,125 upkeep?

If it were a Roman ship and slaves were prisoners of war or criminals whose cost was quite cheap would wages be half or even 1/3 of a Greek ship? Although the initial Roman fleets used free sailors so the cost would have been equivalent.

Anyway- after looking into it I am convinced that most times the upkeep cost would be more than the initial construction costs by a large factor- my impression originally was based on thinking most of the crew other than officers and marines were slaves.