Onthego, driving will definitely save you money. We spent about 165.00 for gas round trip.
We usually leave at 10:00am, but once we left at 3:00pm. I much prefer going morning to morning because by the time the kids wake up in the morning, and the sun comes up, we are almost there. Going 3:00-3:00 almost made it feel like we were driving for 2 days, even though it was still only 24 hours.
As for the route, I am horrible with directions. We got a trip map thing from
AAA and they mapped out the "best" route for us. DH is definitely the navigator of the family (although when he got us lost, I figured out why

). For the most part DH drives. I try to sleep around 10:00pm . I get a few hours and take over for DH around 2:00 or 3:00am, then he gets a few hours of sleep. Really, going down isnt tiring at all because we are so excited, but usually on the day we return we are pretty beat.
We only stop for bathroom and gas breaks, and 1 meal(McDonalds for dinner). We bring lots of snacks for the kids to munch on and my best advice is a tv/vcr combo. Last year DS was really into the shows on Nick GAS so we taped some of those and he was in heaven.
Good luck!