Five things that set the price
Size is the biggest factor. A full casket spray or a large standing spray uses many more stems than a small table arrangement. If you have a budget, say it up front. A good florist will design to it instead of steering you up.
The flowers themselves matter next. Roses, lilies and orchids usually cost more per stem than carnations, mums or alstroemeria. Seasonal and local availability also shifts prices. Peonies in winter, for example, can be pricey or impossible.
Timing and delivery round it out. Rush orders, holiday weeks and longer drives to small towns can add cost. Ask the florist about the delivery fee to the funeral home or church, and whether anything else is added, like an easel or ribbon.