I have stayed both off site and on site and second everthing in the last 2 posts!
I don't know how the costs would compare, but all of the Home-away from home studios have kitchenettes with a fridge, coffee maker and microwave if that is a major concern.
If you want to check out rates and full details, you can go to
http://wdwig.com.
Also, I feel that all the on site accomodations are so well done that it would be a wonderful vacation to just stay at one of them.
Add in the convenience and Disney service and I know that I will always stay on site.
graybill