I've done all the calculations and I can batch about 3L of classic cocktails with just 5 bottles of alcohol and have minimal leftovers:
- 600ml Manhattan
- 750ml Negroni
- 750ml Martini
- 700ml Boulevardier
- 190ml Americano
The leftover dry vermouth (500ml) would keep long enough for me to use in sauces, and the 150ml remaining Campari would just be drunk with tonic water.
Buying everything on Amazon and using pretty decent bottles, this works out to at least 1/2 the price of drinking in Edinburgh bars, and 1/4 the price of London bars.