Saving on the beverage costs at a wedding will first depend on who your catering vendor is. Some vendors require that they provide all the food & beverage for your event. If you have a great vendor, like we did, they will work with you for the expenses on your day and let you bring alcohol, the cake, etc. from your vendor of choice. In Florida, most grocery stores have a liquor store as a separate department so my husband & his groomsmen went to Walmart and purchased the liquor that we needed; our caterer provided the mixes & juices.
If your vendor requires that they provide the alcohol for you, one way to limit the costs is to limit drinks available. For example, provide beer, wine & one or two special cocktails. Maybe you & your future spouse have a favorite cocktail, i.e. mojito or gin & tonic, that you can incorporate in the special day. Tons of bridal websites & magazine have great ideas on how to create a cute name for your special cocktail too.