After the wedding dress and the reception, wedding decorations are what cost a couple the most and flowers are what keep the numbers on the bill climbing. No wedding can do with just a single kind of flower, and depending on who makes them into bouquets or arranges them, will depend on the cost.
One of the easiest ways to reduce the cost on your wedding decorations is to minimize the use of flowers. It doesn't sound practical but it's possible and people manage to pull it off in truly unique ways. The only flowers that you absolutely must have will be in the bride's bouquet. The bride's maids can work with either corsages or a single large flower. The flower should complement their dress and should also comply with the color theme of the ceremony. If the bride's maids are wearing a deep plum then sunflowers will be an excellent choice in flowers.
Flowers are not the last choice in centerpieces either. You give your wedding arrangements a truly unique look by using edible centerpieces like fresh fruit arrangements or fruit bouquets.
If you have floral pieces marking the end of the rows or the aisle; save by putting the more expensive flowers in the middle and adding baby's breath or something similar and less expensive on the sides. I once saw on a TV show where a couple had taken barren tree twigs, put them pots and strung lights on them to mark the aisles. The only cost was on the rent they had to pay on the lights and they used a white runner which was breathtaking.