When you rent a bartender, they are not only lending you their skilled services but also their expertise in their craft. They can make recommendations to you that will at the end of the day save you both time and money.
For instance, a good bartender can help direct you in creating a drink menu that utilizes the same ingredients for different recipes so you can maximize your budget. For instance, if your liquor of choice is rum, your bartender can suggest having Mojitos, Daiquiris, Mai Tai's, and other popular rum-based cocktails.
This way you are not having to select a wide range of bottles for the bar, and can instead focus on having different mixers and some different garnishes.