We have been thinking about your very question. Driving from Austin area to Orlando. Mileage about 1100 lets say one way. Our gas now is projected at $300. We are doing an extended vacation and are going to leave at 6pm after dinner. Will drive through the night no overnight stops. (I work nights so this isn't a big deal) I am a good night driver and so is hubby. Will make the backseat extra snuggly and put kids in sweats to make more comfortable. Kids will have a few new movies I have picked up at Goodwill, Half Priced books, borrowed etc. Ipods with Disney podcasts loaded for listening and going to the library for books on tape. So I consider those costs no biggie and not worth counting. Will also pack some yummy goodies for snacking - oatmeal chocolate chip cookies, banana bread, etc. An early, early morning breakfast for a rest stop and then late breakfast somewhere like Denny's. Will pack a lunch since we are going to need to go to grocery store before resort. We can eat for family of 4 for $25 at Denny's.
Then on the way back. Leaving in the morning. Eat at hotel room (we are staying offsite). Stop for lunch at restaurant ($30) then another stop for dinner ($40 on the high side). Again good snacks for the road, printable games for car, coloring books, other books on tapes, etc.
TOTAL costs:
Gas $300 if goes up to $5 by Nov then $550 (but airline prices will go up too)
Food on the road $100
Snacks from home so in grocery budget
Books, movies, etc. Can be free if you go to library, borrow etc.)
For us the $650 instead of $1100 for plane tickets gets us into Cirque and Hoop De Doo. That's worth it to me!
We are staying for 12 days and so we are cooking at the resort and will be driving to some places at Disney. It is worth it to us, but can understand why some people say no go.
We are also packing a lunch into Disney on some days just to save a little money so we can stay longer.
The price of a table service restaurant at Disney is one night at our hotel so that is a big savings. Hope this helps.