Offsite definitely has a lot of options. We and I have saved a fortune by staying outside the bubble most trips. And for longer trips, especially with older kids, definitely consider renting a condo or house at Windsor Hills, Windsor Palms and the like. That ability to spread out a bit can be priceless.
One thing to remember when staying offsite is that you really need to rent a vehicle. Don't get enticed by the hotel having a shuttle that runs to the parks...do that and you're on their schedule, not yours. When you do the math of comparing the cost vs. staying onsite, remember to add in the cost of your rental vehicle, $22 per day to park (unless you have an AP) and gas and tolls. But, you can also subtract things like having breakfast (and maybe more) in your room, offsite dining, etc. The amount you can save on even sometimes eating dinner outside Disney can easily pay for the rental car.