Would you agree that somewhere on the Internet I can find that bartenders on cruise ships are making far more than $1000 per month?
In addition, your 3000 out 4000 passengers may be far too high. You have to exclude anyone under 21, and anyone who declines the drink package. For example, that would be 3/4 of my extended family who might, might have a glass of wine or a beer at dinner.
Finally, you have no clue who is included in the receipt of the drink package gratuities. How about the MDR servers who bring 4 drinks to the table? How about the runners who stock the bar? The staff that washes the bar glasses? Maybe the laundry staff who wash the bartender/server uniforms?
Point is, it's all pure speculation.