Question for Florists

I would like to know why florists have one set price for bridal bouquets. What if I only want to have a single rose or something like that to walk down the aisle with - is that going to cost me $150 too? This really aggravates me! Everyone seems to have one particular price that they give for the bridal bouquet! I want an explanation!

Sorry if I sound annoyed - just very frustrating - they don't even know what I want yet and they tell me $150 (or around there)!

Thank you!