Just for kicks, I priced a WDW vacation. A family of four, my DD is now 10 so that means an adult ticket for her. DS will be 3 in Januray so that means we'll have to pay for a ticket for him. We always stay off site at DL because I can't justify the cost for a DL hotel. A 4 night/3 day park hopper vacation for us runs $1200 booked through disney travel. I crunched the numbers and found if I bought hotel and tickets seprate I could drop the cost to $950. We use disney travel because we are able to make payments.
A 8 night/7 day no hopper vacation for our family at POFQ would run over $3000( again through disney travel). That doesn't include food or airfair. Staying off site, booking hotel and tickets separately for the same amount of days and same month (may) I dropped the price to $1600. According to reviews I've read the hotel I was looking has more sq footage, softer beds, and plushy pillows. Kids eat free breakfast buffet and use of DTD buses (also run better than WDW buses).
Then I have to add air from CA to FL (we always drive to DL) and food. So, for the cost of just hotel and tickets through disney travel, We can have the whole enchilada if I book everything by itself and stay off site.
Yes, it's often much cheaper staying off site at WDW....but a few things to consider:
Transportation to the parks from your offsite home.....DL has so many off site hotels that are in walking range. At WDW this is not the case. You'll either need a rental car (parking fees apply unless you stay on site or have a WDW AP). Some hotels do offer shuttles...but be sure to check how often they run and how early/late they're available.
Another choice, besides the hotels off site is to get a vacation home/condo. I know when I first heard that choice I assumed it was too expensive, but was very pleasantly surprised to find that very often it's as cheap as one of the tiny hotels off site, much better maintained, bigger because it's a home/condo not a single room with a bed or two, and of course has the full kitchen and a free washer/dryer in most cases. We've done this a couple times and have used vrbo.com (vacation rental by owner). For instance, I just went to vbro.com and plugged in Disney World....there is a 3 bedroom HOME for $70 a night. Windsor Hills, a condo resort that is always very highly recommended here on DIS has a 2 bd for $75 and is among the closest to WDW. Some have shuttles.
Now, we've also stayed on site....and it's very cool to immerse yourself in Disney everywhere. The deluxe hotels are pretty pricey, but the values and moderates are well maintained, fabulously themed and frankly, only a few square feet smaller than the deluxe and they cost a more reasonable amount. That cost depends on when you go of course, but it's not unusual to find deals in the $60-70 range for a value and less than $100 for a moderate. Their regular rack rates are about $100 for a value and $150 for a moderate (again, depending on when you go). A 10 year old is likely to LOVE the over the top Disneyfied themeing of a value....but the moderates are really beautiful as well, just a little less in-your-face Disney theme, they are themed to a specific style...Port Orleans is Civil War era manor houses, Caribbean is very tropical in color and landscape (and they have some cool Pirate themed rooms for an added cost); Coronado is very southwest is color scheme, etc.
Another deal to watch for is when they offer free dining. You have to pay full rack rate for the hotel room, but you get that $45 per day dining plan included. And the dining plan at WDW is worlds apart (pun intended) than DL....with the WDW dining plan at a moderate hotel you get 1 Table Service, 1 Counter Service and 1 snack each day. At the value hotel you get their Quick Service which is 2 Counter Service, a snack and a free refill mug (free refills for the length of your stay at the Hotel food court...soda, juice, tea, coffee, hot cocoa, etc). You can pay a small charge per day to upgrade to the same plan as the moderate. There are over 100 Table Service restaurants, so unlike DL, most people do a Table Service every day. At these TS you get your entree, non-alcoholic drink and a dessert. This very often is more than the $45 cost of the dining plan. There is also a Deluxe Dining PLan (which is what the free plan is at the Deluxe hotels) that you can upgrade to from a moderate or value. It gives you 3 meals a day, your choice of whether to use them as Table or Counter, 2 snacks and I think the mug too....but most people who are not die-hard foodies find this too much food! This is the first year that Disney has offered SO MANY free dining dates....originally is was only early Fall, then a couple years ago they added in some November/December dates, and for 2011 there are literally hundreds of dates for free dining.
If you stay off site you can't get the dining plans....and food cost is very similiar to DL, though you have a lot more choices!
Yet another option, which I can't really help with because we've never done it, is buying points to someone else's Disney Vacation Club timeshare. There is a whole section for this on DIS boards.