Also for a rental car, try autoslash.com It is really great and offers discounted rates with popular rental companies. In my experience, rental car rates always go down closer to the rental date, so a rate that shows today, could be half price by the time you rent the car. Always check the rate up until the date you leave.
One thing we found with driving is that if you are stopping "mid" way, you should try and do more then half the trip the first day. The second day, everyone seems to be more tired and just wants to get to Disney. We used to drive from NJ for 12 hours the first day and leave only 5 hours for the day of arrival. Not saying you have to drive that much but try to do more the first day, definitely makes to trip easier.