Serving Alcohol at a Restaurant Wedding

I am having my wedding at a private dining room at a restaurant venue. For people who have done this, what is the cheapest way to go about serving alcohol? The open bar packages at the venue come out to be way more alcohol than what we think our friends and family will actually drink, so we are going with a consumption bar and we can limit what is served however we want. I don't really want to make it a cash bar, so I'm looking for any advice on what limits to place on the drinks that are served and how long the bar is open so that we can keep the cost down without making our guests pay for their drinks. We are only having about 50 people but most of them are friends of ours who drink. Should we do a signature drink only, signature drink plus wine & beer, drinks only during dinner service, drinks when the dance floor is open, etc.? Any advice on what worked well for others would be helpful!