While saving money on the meal is great when you are working with a limited budget, adding to the guest experience is important as well. There are ways to do that without spending a lot (or any) extra money.
One of these is to serve family style. In a way, this is a cross between sit down and buffet service. Large bowls of food are placed at each table and the guests pass the dishes around, taking what they like from each, resulting in more interaction between guests than other serving styles.
This tip is from the Dream Wedding on a Dime; 7 Secrets for the Budget-Savvy Bride ebook.