How much should I sell a 20 ounce water bottle of absolut vodka for?

I am a minor and my friends and I are using it next week (in addition to beer). They charge me when we use their stuff, so I was wondering how much I should charge them? Please no lectures. I am completely at ease with my choice and I don't let drinking interfere with my school/family life at all.|||$20 is a good starting price.