Bridesmaids dresses can be rented. Some formal wear shops will offer a discount - i.e. groom's suit free with rental of groomsmen's suits. The ring pillow can be made or borrowed. Items like cake knife, toasting glasses, cake top, etc. can be borrowed, rented, or purchased used. Carefully control the size of your guest list.
Daytime receptions are less expensive than evening ones.
Serving punch, cake and snacks will be less expensive than a full meal. Schools will often supply the service for the cost of materials - bakery programs, floral arranging, etc. Have the flowers do double duty - use them for the ceremony and reception. Simple flower arrangements and bouquets, tastefully done can be every bit as attractive as more elaborate ones. Buy supplies through wholesalers when possible.