Also keep in mind that even if you book now, you can still get in on new promotions that come up (so long as you are still eligible) but you MUST call Disney yourself to get them. Disney won't apply them for you.
$5,500 including round trip plane tickets for a Deluxe resort over 6 nights is pretty reasonable. It's a lot (I'm not usually a big spender either), so other than the above, here are my other money-saving tips:
- Start saving change as well as odds and ends of cash that you find in pockets when doing the laundry or laying around the house. Put it in a jar for "vacation money" and use it for souvenirs.
- Make a list of "must have" souvenirs so you don't go nuts buying things in the park (trust me, this happens).
- Downtown Disney has a lot of stores that have similar items sometimes for better prices, especially if you want things like ornaments or clothing.
- Look on your receipts after you eat your meals in the parks. Sometimes they will have coupons for 10% off at certain stores if you shop early in the day. Save these and have a little shopping morning.
- I never bother buying Photopass pics. You can just ask the photographer to take a picture with your camera as well, and they will usually let you do it, especially if you hold still for another 5 seconds so they can take their own picture. After all, it's what they're there to do.
- Like someone said, do the
Disney Dining Plan. This is definitely worth it to do the regular or quick-service dining plans.
- A lot of moderate resorts are very nice, although I totally understand wanting luxury for your honeymoon. However, you really will save a bunch of money by aiming lower.
- Maybe try another deluxe resort? The Polynesian is one of the more expensive resorts to try. Wilderness Lodge or the Animal Kingdom Lodge are slightly more affordable and still on the high end of things.
- I wouldn't bother with concierge level unless there is something really compelling about it such as a special tour or something you must have. You'll be out and about most of the day, and unable to take advantage of some of the best parts of concierge.
Another question for you: What did you want to do at Disney? Rides? Dining? Spa? You know there is also a Honeymoon Registry you can do if you want wedding guests to have the option to help you with the honeymoon expenses. IMO this works better if you don't want/need other registries, and if you have a lot of experiences in mind for the two of you.
There is no way a 6-day trip to Disney should cost that much, especially not in September, which is Disney's low season. There is always some room discount available, whether it's through 
Have fun planning!
