Reception Flowers

I'm just beginning to look into flowers and have not been to any florists as I'm still trying to talk to people about where to start...I know that I want simple rose bouquets for myself and my bridesmaids (I can't even think about what to do about the chuppah), but there are a lot of allergies in my fiance's family so I was thinking about going with branches (i.e. dogwood) for the reception. Is that more or less expensive than regular flower centerpieces? Let's say compared with roses, hydrangeas, etc...no orchids.

Would really appreciate some direction as I'm working within a somewhat limited budget for more tables than what I would have liked to have (20ish).

Thanks to anyone that responds!!

Oh yea...the wedding is May 29th