How many guests?
Where?
What affiliation?
Do they want a regular standard style wedding?
Do they want to significantly cut costs and be unconventional?
There are the basics that must be paid for.
Hall
Food
Music
Flowers
There are gemachim for silk flowers.
A keyboardist will be cheaper than a band and there are some who give special deals to those in need.
Catering is according to the number of guests.
A hall that is less central will cost less. Obviously, the "destination" ones will be more.