Invite your other guests to an open house afterwards. At the open house have a buffet of finger foods and light refreshments. You can pick them up at a store like Costco, or make them yourself. Sew your own dress . If you can't sew, find someone who can.
Many seamstresses are very reasonable in their prices.
You may be able to cut the cost by doing some of the work yourself, such as sewing on beads. Keep the affair informal . Limit the number of your bridesmaids. Let them wear what they want. If they want to buy a new dress, fine.