Help!!! Idk how to do the bar

The most cost effective way would probably be to purchase it yourself at a place that takes returns if bottles/cases are unopened and then hire a bartender to man the bar. You could also look into bartending services in your area and see what they would quote you for providing the alcohol/drinks/garnishes and supplies and see if that would be more worth it for you. Remember to factor in the time you'll need to purchase all those things and that you'll need a place to store it.