Well, when you think about it, there's quite a bit involved in a corsage. (And in boutonniere or any other floral design for that matter. But for this post, we're just going to concentrate on corsages.)
First we have to coordinate the design to you (or your date's) dress style, dress color, and personality. It really wouldn't do for the outgoing girl wearing the latest designer dress to have a traditional corsage with miniature roses and baby's breath, or for the vintage-wearing artistic girl to have a contemporary arm cuff with minimal florals. So part of our job is to delve into the mind of the person ordering and to determine which floral art piece best goes with which girl. Dress / personality style is just the beginning. We also look at dress color, jewelery color (our silver arm cuff may not match your bronze choker and coordinating stilettos), type of flowers, and of course, budget.
Second, we don't make your grandmother's corsage! We're creating floral jewelry, complete with a keepsake bracelet (no more elastic wristlets). We also don't make cookie-cutter corsages. Each piece created is unique, just as each flower is unique.
And then there's the technical aspects: materials, time, and skill. Yes, each of these comes with a price tag. We won't lie about that. Each corsage physically contains some or all of the following materials: ribbons of various sizes and materials (sheer, single face satin, double face satin, picot, etc.), wire, tape, glue, crystal accents, pearl accents, decorative wire(s), elastic band or keepsake bracelet, permanent foliage, fresh foliage, and of course FLOWERS.
Then, to make a well constructed corsage takes time--both when making the specific corsage and training time and practice time to master the techniques. Which translates to skill. Making a well constructed corsage is not something you get right the first time! It takes practice (i.e.time). So part of your cost is for the time it takes to make your corsage.
Finally, the creative aspect. The non-physical part where I know this piece fits here and not there. Part of this comes from training, part from practice, and part from having the artistic 'eye' for flowers. I can make a pretty good chicken pot pie but I'm not a chef. I can take an OK photo, but I'm not a photographer. I just don't have the eye (or taste bud) that turns my cooking or my photography into ART. Yes, a portion of your cost is for my artistic ability.
Can corsages be expensive? Sure they can--if you're only looking at the price tag. But what you end up with is well worth it: a personalized floral creation unique to you. Styling, individual design, materials, time, skill, and art--whether a gift from your date or the final accessory you've picked to compliment your ensemble, what better way to complete your (often) first formal event?