This day and age I would not bother with large flower or dried flower arrangements, They are clearly too expensive a luxury.
I would go to a local flower wholesalers and buy two Kilos of simple potpourri three months before I was due to do the planned event I would buff up the potpourri from the wholesalers with dried lavender and rose buds from my own garden. You do not need fixatives or preservative for lavender and rose buds but you must know the secret for drying then or they will rot.
I would make up a thousand bags with 3 fragrances ie Peach, Rose and Jasmine and sell then at 99p. a a bag . They would sell.