It is easy to say "Business is business", but in reality, it is really hard to say how much you would like to charge from what you do for your friends. People always think that what you do for friends should be called "help" instead of "service".
Good advice so far.
My take on this is to estimate how much you would spend on a gift for the happy couple if you were just another guest, and discount your normal rate by that amount. People tend to overlook the fact that you're working at a wedding, not dancing about, drinking and enjoying yourself like everyone else.
If you were a florist, a hairdresser, a dress maker or put up marquees for a living, would they expect you to do it for nothing?
You should be paid - No question!
The day you think you've found perfection is the day you stop looking, then someone else will find it and move in front of you.