What is the average cost of liquor?

This varies greatly. It depends on the type of alcohol (i.e beer, malt liquor, wine, vodka, whiskey, rum, etc) and the quality of the alcohol. For example, you can by a 6 pack of low alcohol content beer (i.e Keystone or Busch) for around four dollars. Or you can buy expensive, high-alcohol content beer that has is a rich ingredient brew (i.e Guiness, Michelob Amberbock) for $8 a 6 pack. Vodka ranges anywhere from $8 for a fifth (Burnettes) to $20 for a fifth (Smirnoff). Evan Williams whiskey is much cheaper than Jack Daniels ($20+).

Over half the retail price for a bottle of distilled spirits (vodka, gin, rum, whiskey, etc.) consists of taxes.