Check out the
AAA trip/gas calculator to see approximately how much driving will cost you.
http://fuelcostcalculator.aaa.com/ We always add about 20% on to their estimate to account for driving around Orlando while we are there. Depending on your vehicle, you could easily be looking at $500+ just in gas charges.
Of all the vacation elements, i think food is the easiest one to find ways to save significant money. Consider checking out restaurant.com for great deals on vouchers for locals restaurants. Some of our favorites are BB Kings and Giordano's. I would suggest buying a voucher with enough credit to order stuff to take back to your place and use for lunch/dinner the next day. We fed a group of 7 last year for 2 weeks on a $800 budget including eating at Boma one night for dinner. We shop at Publix for groceries and eat very few counter service meals.
Accommodations are the other easy way to save money. You have received lots of great ideas here for places to stay. I would strongly consider staying somewhere that does have some level of kitchen available otherwise you are going to spend well over your budget on food.
Even after using a ticket discount (like the one in the Mousesavers newsletter) you are still looking at at least $1,300 for tickets (assuming at least 4 park days) Have you considered going to Universal instead? You can have more park days there for less than Disney. Your boys seem like the ages that may love it (mine are 10 & 11 and have been in love with US/IOA since we started going there 3 years ago.)
All together (and bare minimum) I think you would be looking at the following
Driving (gas/tolls/etc.) - $550
Food - $300 (mostly groceries but a few less expensive meals)
Accommodations - $500
Tickets - $1,300
Misc - $250
So you are looking at at least $2,900.