Optimistic 1 bottle of 1l of gin weekly makes it approx. 3 shots daily, which seems reasonable to me, considering 40% strenght. Secondly, let's be optimistic again and say, he doesn't drink a week in the month, making it 3 bottles monthly. This means it's 36 a year, so round it up to 400 ginnies at 11 years with all of the optimism. His liver is prob tougher than his brain dood. Eyeballing a Beefeater gin at 12$ (prob the cheapest drinkable substance slightly resembling gin) makes it around 5k spent on gin. And that is just with all of the optimism.
Also, your approximation is just about 1,75x of mine in the bottles and 1.75 times in volume, so lets say its 3.5 times as high, that gives us the range of money spent between 5-15k, considering your approximation as the worst case scenario and mine as the best one.
Midfirst bank with 5k debt says hello