Floral centerpieces are a traditional way to decorate your tables. Use any kind of container, from fish bowls to baskets, tea pots to tennis shoes. If you are using silk flowers (this will save a lot of money) you can make your center pieces well in advance of the event.
If you are using fresh flowers, you can still cut the cost by using an online wholesaler. Many wholesalers will sell to individuals, and you can order everything from tropical flowers to traditional flowers. Do an online search for wholesale flowers. Remember when using fresh flowers, you will need to be sure your container is water proof. Be sure to soak your oasis foam overnight before arranging the flowers.
How about using a hanging plant as the centerpiece. Remove the hook and wires that you hang it with and set it in the center of the table, arranging the long tendrils to flow toward the outer edges of the table, Insert a pillar candle in the center of the plant if possible, or add other accents. Give the planters to any guest you choose.
What about painting clay pots to match your colors, and planting live plants in them. You can use begonias, mini roses, geraniums, pansies, mums, carnations, herbs, just about any plant. If you start about 6 months before the event, you could have very large plants for very little. Buy the plants at a garden center in flats, and plant them in the pots. Dont paint your pots till closer to the event. This centerpiece could be as little as $2.50 per centerpiece. Give the planters to any guest you choose.