Happy is right, it depends on where you want it to be. On the console, under the steering wheel, on or in the door pocket or even beside the seat.
Lots of options, just make sure you can reach it without having to strain or do something fancy. If the seat belt is retracted it could pose a real problem.
The Kydex ones are simple to make and hold up well for solid mounted car holsters. Leather is a little harder.
+1 for wanting to stage your gun while in the car, I am a big supporter of this idea for a few reasons, one is I don't what my gun flying around in the event of a wreck, two I don't what anyone to be able to tell if I am drawing my gun from the holster, three I don't want to have to fight to get to my gun in my carry holster.