Definitely make a list of everything you may need to pay Disney for that would go toward your minimum expenditure. The sooner you can do this to get an idea, the better, as if you realize you may want to go with outside photography, the earlier you can book, the better! When are you getting married?
To help with your list, I would highly recommend the Disney Passporter for Weddings and Honeymoons, Carrie (
@lurkyloo ) is the author and it has all the information you could possibly need. Get the e-version, any time it's updated you can download the update for free.
Little things can add up. Using myself as an example, we're planning very minimal decor, Ariel's doesn't need much (no flowers, and I'm having my bouquet made out of park maps, not through Disney), but I imagine centerpieces will cost us at least a couple hundred, even if we make them very simple. Then we will have a DJ (~$1000) or iPod hookup (~$300-$500). Many of our guests will be staying at Pop or POFQ, so we'll need to transport them to Sea Breeze Point and back from Ariel's. Unless all of your guests are staying where your events are, it is customary to provide them with transport. Or if everybody is staying off site, then you tell them to drive themselves. A good number for us will be staying at Beach Club and some off site, so at least we can save there. Not sure where you're having your ceremony and reception.
If you do decide to stick with DFAP, make sure you research each of the photographer's work/style to see which you think would be the best fit for you. Then give your top 2 or 3 to your planner as your preferences.
Good luck!