I think I might say something like, "I can't provide receipts for every cost that goes into making a wedding cake. I am sorry, but if you need that to ensure fairness, you'll have to find someone else to make your cake. I would encourage you to call some other bakers and get pricing for the type of cake you're looking for. If you do that, I am sure you will discover that $2 a serving for a fondant covered cake with all of your details is WAY MORE than fair."
I have to be honest though. The statement from her leaves a bad taste in my mouth and I'm not sure I'd be as diplomatic as I've encouraged you to be.
Good luck and please keep us posted!
Thank you! That really helps a lot! Yes the $2 per serving is VERY CHEAP for what she is asking! When I talked to her last night, I had to keep my temperment in check because I just about flew off the handle. Glad I waited and found everyone here to get a better idea of what to say. Thanks to everyone!