I would not give out an average cost of a wedding at all to be honest. I only give prices at consult and when i am asked how much does a wedding cost i just say how long is a piece of string.
They could have 2 bridesmaids they could have 8. They could have 40 guests which equals 4 tables they could have 150... I think you could easily drive a bride away by giving an average. At least when you give them at consult, you are talking the talk and doing the sales thing. She also knows as you go along what she is paying for each item.
One little thing i do is when i give them the final figure i read out everything so i say "right the bill is... and that is for 1 brides handtied bouquet, 4 bridesmaids bouquet, 2 mothers corsages, 100 buttonholes, 10 table centres," etc etc I give them the full title so that the list seems longer and when they get the price at the bottom it seems for a lot anyway. Also i then add so thats how much it is for all your wedding flowers, all your venue flowers and your chair covers. This way its like they dont have another bill anywhere else if this makes sense.
And then i cross my fingers under the counter that they book (i think this helps lol).