Well, if you're crazy, I'm right there with ya'!!

For us, it is not only cheaper to drive, it is a heck of a lot easier.
Twice a year we do long drives. All my kids did a 20-24 hour trip at 3 or 4 months of age. And they've all had a long trip in the middle of their toddler years. With a little foresight and the right attitude, you can enjoy the drive.
Attitude is number one. The first thing you must remember, when you choose to make a long trip via car the car ride isn't just your means of transportation but part of the trip. Keep focused on having a good time not just making good time. As a matter fact, that leads me to foresight tip #1.
It's not that it is the first thing you will do, but, imo, the smartest thing. Stop often. Take lots of breaks. We never drive longer than 3 hours when the kids are awake without a stop. It could be at a gas station when diapers are changed and bathroom breaks are made, or my favorite--at the rest stops. DH leads a little mini aerobics class for them when they turn 2+. It's stretching and running. For the littler ones its wandering around. No stiffness builds up, energy is worked out, curtails whining before it starts (for the kids too

), a major mental break from looking out the window, etc. It's the smartest thing we ever did. And we stop for every meal, preferrably where the kiddos can get out and run around.
My next tip is timing the drive. I nap during the day we leave, doing something with the kids (preschool/school, dropping off with a friend/my mother) so that I don't need to worry about it. We then leave at about 5 pm at night. We drive for a few hours, get out for dinner, drive for a few hours, hit a run-around spot, drive for a couple more hours, kids & DH sleep, I drive. This is where we make our time. When I'm too tired to drive, DH and I switch off. And then again when DH is too tired, we switch again. So on so forth. If and when we are both too tired, we'll stop for the night and sleep. In the morning we'll stop at a rest stop (if we didn't get a hotel) and clean up (wash faces, brush teeth, etc)--helps to make you feel normal. Amazingly enough, we are never tired upon arrival. Of course, none of us have problems sleeping in a car. Heck, my kids would sleep on a fence post if they were tired.
Which brings me to my next set of tips. Prepare for the car ride. We all have travel pillows and blankets. The kids have someplace hard to put their feet. We bring the special stuffed animals. We bring a long a few favorite toys that keep them active (even at 12 months you'd be amazed at how much time a magna doodle kills). We bring along a few new surprises. We have coloring books/paper and markers/paints/crayons--crayola color wonder anyone? I have print outs from online in a notebook & pens/pencils for each child old enough. I have travel games--bingo, madlibs, etc. And, of course, the DVD player (with bunches of Disney movies for trips to WDW). We have tons of childrens music on books on CD.
We have a cooler packed with smart snacks (nothing too salty, etc) and drinks (good idea to avoid caffiene). We bring along lysol, oust, lots of baby wipes (those things work miracles), paper towels, toilet seat covers, soft soap, anti-bacterial wipes, jumper cables, fix-a-flat, small (scented) garbage bags, flashlights (and seperate reading lights for the kids), road maps, etc. I have a backseat diaper changer thing from Target--just gives you a flat surface that is sanitary & keeps you out of the rain--for when we have one in diapers. I let all those who are fairly new to potty training (under a year trained) wear a pull-up just in case. It sounds like a lot, but really doesn't take up too much room. I have all toiletries backed in a bag that stays in the car, along with a bag of changes of clothes--the smaller the child, the more changes of clothes. Everything else goes on top of the car.
We throw out trash at every stop and I make sure to vaccume it out before the return drive home. Keeping the car free of clutter makes it just a way smoothier ride. Don't let people scare you away--I've found most people who have told *me* not to do it, have never even tried it themselves. Good luck and happy driving!