Princesses typically require plenty of assistance, but you shouldn't have to pay extra for it.
Ask your royal bridesmaid, the queen mother-in-law or even the prince/groom for assistance selecting and creating your bouquet and flower arrangement. It'll be much cheaper than paying a professional florist or wedding planner, and nothing says royalty more than telling your loved ones what to do.
If hiring a florist is a must, create a budget and ask your pro to respect it. For help getting started with a professional florist, brush up on what qualities you should be looking for in 5 Tips for Choosing the Best Wedding Florist.