A great way to save in the wedding budget is to trim down the bar. Do not do a cash bar. I repeat. DO NOT DO A CASH BAR. It is tacky – would you ever host a party and ask people to bring their own beverage? No? Well, don't do it at your wedding either. Plan for the drinking but make effective choices with the offerings and keep the bar budget managable.
The easiest way to accomplish this is by limiting the selections. One red wine, one white, two beers (one light and one regular), and one cocktail.* Estimate the set amount each person will drink, buy that amount, and (if it runs out) have the bartender make a tactful excuse ("safety first!") and switch people to water or soda.
Here's some good cocktail suggestions from Serious Eats:
*Remember your non-alcoholic drinkers and provide water, soda, and a virgin option of the cocktail.