Flowers.

Florists can be very expensive. If you're a creative person (or you have one in your life) then consider doing your own flowers. You can get them in bulk and have them delivered a few days before the wedding. Then you (or creative friend) can put the centerpieces, bouquets, and boutonnieres together. Make sure you have lots of fridge space to keep them fresh.

My friend did this recently for her wedding and she got hundreds of flowers for less than what you'd pay a florist for just the bridal bouquet and the bridesmaid bouquets. She got a TON of flowers for very little money. If you want a lot of flowers and you're on a budget, this is the way to go.