Last time I went to Costco, a handle of Makers ran me $36. Since I have no other hard figures, I'll assume it would cost the airline the same amount despite massive volume. Even someone who hits the alcohol moderately hard and packs away, say, 6 drinks during a 2-3 hour layover would consume about $5 worth. Sure, you could compare it to an airport bar and say that tab would have run $75, but the fact that the day pass visitor "only" pays $50 isn't why they don't serve better liquor. It's because of the members who they serve the stuff to all year long for a rate much lower than what the day pass visitors are paying.