Only tourn I've entered on a ship was TX Hold'Em on RCCL and the buy in was, I believe $125. of which I think the house kept $25.
These were typically 7 player tourn as that's how many can be seated at the only table. So there was $700. in prize money for the winner each time. On the last night of the cruise there was enough demand for Hold'Em that thay converted one of the blackjack tables as there were plenty of empty seats at the multiple BJ tables. They're pretty good at improvising if there is demand and more revenue visible for the ship.