Opinions please!! How much should I charge for doing someone's wedding flowers???

[shimmyshimmy83]

I was recently recruited by one of my mother's co-workers who is starting an event planning business. Her first event is a wedding and she has asked me to do all of the floral work for the wedding. I have roughly 6 years experience in floral design, having worked in various floral shops and have done many weddings before. Problem is that when I worked in the shops I always recieved my normal hourly pay. This will be my first independent floral project and I am unsure of what to charge.

The floral arrangements we have discussed thus far will cost roughly $3,000and will be divided between 20 table centerpieces, bridal bouquet, 5 bridesmaid's bouquets, altar arrangements as well as pieces for the groom & groomsmen.

They have requested that I be paid in one total amount as opposed to hourly.

So here's where I need your opinions:
Should I ask to be paid a certain percentage based off the final cost or come up with a price beforehand? Also what percentage or amount do you think I should be paid? I don't want to under or overbid..

I don't want to ask anyone in the floral industry as from my experience topics like this tend to ruffle feathers...

I've also posted this topic on the wedding board in order to gain as much advice as possible.

Thanks in advance!