Our daughter got married at WDW in 2008 - the way we approached cost was as follows:
We set a total budget - it was the same amount of money to be spent whether the wedding was at "home" OR at WDW - so in the end DD got the wedding of her dreams and we didn't have to take out a second mortgage
Agree with PP - look at the packages on line and get a rough idea of the cost - if you think you can compromise with things like expense of wedding gown, number of guests, food/beverage options, flowers (do some DIY stuff) - you will probably discover it's the same (or close to) $$$$ for WDW as it would be anywhere else -
For us every penny was worth it because:
A - DD got exactly what she wanted

B - Every detail was expertly handled by the planning team at Disney

C - The event was something unique that she and we still talk about as one of the best days of our life (next to her being born and graduating from college)
In fact, we felt it was such a great place to have a ceremony - we used the Memories package ourselves last year for a vow renewal!
Good luck and cherish this time planning with your daughter - wherever the wedding is held
