There was no dirt hauled in at all, this is kinda the way it was done.
1. Boxblade used to scrape off the top 1" to 2"
2. Ground ripped to about 4" deep and then all of the loose soil scraped off.
The fist two inches of dirt was taken to the back of the property as it was full of seeds and weeds. The first 4" of topsoil that we scraped off was piled up on one side of the track. This is our reserve of dirt, The dirt is also "rotated" with every track rebuild. Meaning that the dirt we used for the current track will not be used for the next track. The dirt gets used for every other track rebuild if you get what I mean.
We buy the drainage pipe in the large rolls. I think they are 200? maybe 300? foot long. I think we started with about 6 or 9 of these rolls. Our current track does not use all of the pipe so we always have some spare lying around. The roll cost about $30.00 or $40.00 dollars apiece.

4" pipe i would use in the straights, if a car hits it, it will usally glance off it.
6" I would use in the corner, less chance of the car jumping the pipe.

If anybody would like to see the track in person, we are having our biggest race of the year on the 21st of April. We are expecting at least 100 cars for a one day race. So if your close to eastern Oklahoma that day stop by and see us. Our flyer is posted on this fourn some where.