Lisianthus

That's a big guessing game with lizzie.It all depends on how the flowers come in and the price you are trying to hit.Average size 2 bunches
 
I use lizzies in wedding bouquets often, and have found that you can only count on a single bloom per stem, plus a nice fat bud. If you want all open blooms and aren't mixing in greens, I would get 4 bunches. If you want to incorporate the buds and/or are using greens, 2 or 3 should do it.
 
I agree with snapdragon, I would get 4 if it was only lisi, they just don't take up enough room if doing a handtied.