When my husband and I got married seven years ago, we were determined to have a wonderful, yet debt free, day! One of the things that we did to save money was to use potted plants that were in season to decorate, like marigolds and other "autumn" colored plants. We purchased my bouquet, groom's and groomsmen's buttonhole flowers, and single stems for the bridesmaids from a florist, but all the other flowers came from a local nursery.
We had an outdoor autumn wedding, so we took purchased cornstalks and hay bales to decorate the entry ways to the tent (the tent was an expense but worth every penny for a reception site and as a backup ceremony site should it rain). The hay bales helped to disguise large plant pots. Smaller pots were "prettied up" with swatches of cloth or lace, and at day's end, the plants were given to our moms and grandparents.
I am not blessed with a green thumb but I suppose to cut expenses further you could grow the flowers from seed. I would suggest stashing cash away, however, in case the plants do not thrive. If the plants do well, you will have that much more money to spend on your honeymoon or to put toward other expenses.