If you get married around Easter, there is likely to already be flowers at the church. Flowers such as tulips and lilies are more likely than others. Check with the church before you spend money on more flowers. Also, check to see if this works around other holidays.
When you book your wedding, see if there is another wedding right before and/or after it. If so, see if they will let you contact the other wedding party to see if they would like to go in together on the cost of the flowers that you use at the church and have the flowers be available for both weddings.