For 100 people I would do an 8-10-12. They provide the fresh flowers so you don't worry about that cost.. but I charge $4/serving for buttercream finish cakes.. so that'd be $400.
HTH's a bit. It's a pretty cake.
As I remember the closest you will get to that # of servings is 110.
A 12"; 9" and 6" round should do it.
As for pricing, since the cost of ingredients has gone up sooooooooo high in the past 6 months I'd say $3 or more per serving.