I did wedding planning for many of the brides I sewed for. The best thing to do is sit down ahead of time and plan out what you ARE going to spend on what. If you only allow yourself $500 for flowers then you fit the flowers into that budget. DON'T try to fit the budget to the _______. This is a good lesson for married life too. Set a budget and stick to it. Sure there will be times when you will go over a smidge, but don't get used to that.
Remember to that this is your day or it is your sandbox -- if nobody wants to play by your rules they can go play on the swings!
Hope things get easier for you soon.