Well, it really depends on what you are wanting to do, where you are wanting to stay, etc. You can get a room at Disney for around $100 a night, then you would need to add on tickets. It would depend on ages and what type tickets you want. The commercials advertise $1500 for two adults, one child, and one junior for seven nights and that includes tickets. Plus, Disney has free dining right now if you go during their promotion.
If you want to stay off site, you may save a little money. But the hotels usually aren't as nice as Disney, if they run less in price. Plus, you don't get all the added benefits of staying on site. You could also look into a vacation home rental or timeshare.
To give you a very estimated guess, I would say maybe around $5000. But this is a very rough estimate.
I would go to Disney's site, where you can price a stay http://www.disneyworld.com or contact a travel agent. That way you will get a more accurate price and get what you want included.
Hope this helps!