It took us about 16 hours total, split over 2 days.
We left at 3:30am and was in Brunswick, GA at 4:30pm. That includes 2 x 1 hour stops for breakfast and lunch.
We wanted to get past DC before rush hour and that was great. The roads going down were very, very quiet. I tried to stay between 10-15 mph over the posted speed limit. MD - 55/65, VA - 55/65, NC, SC, GA - 65/70 so we were making good time.
If you have a radar detector - use it. We were lit up 4 times and had the early warning.
We then had an easy 3 - 3.5 hour ride to Pop Century.
No tolls for us, but we used 3 tanks of gas, so figure about $90-$100 for gas and 75 for hotel.
Not as much as a flight, but make sure you have something to keep the kids occupied. We had the portable VCR - recommend it highly, and coloring books.
I would not mind driving again, because when it was time to leave, no need to pack, just chuck it all in the van, not like a flight.
Plus with the van we had the luxury of having a vehicle there, if we needed it.