Not sure how passengers paying $18 per day vs the normal lowest price of $42 per day will result in a banner year income wise for the bartenders.
18% gratuity for $18 per day is $3.24 per day vs the $7.56 per day in gratuity based on a $42 per day price. This would seem to indicate that every passenger that got the $18 price would need to tip an additional $4.32 per day over normal extra tips just to bring the gratuities in balance with normal prices. Seems to me the bartenders will be in for a banner year working more and earning less in tips. Of course these numbers all depends on how many people got the $18 deal.