Why do you need to replace the steering column?
If you have a broken shifter housing, which is the most common problem with Aerostar steering columns, then replace only that. Most wrecking yards have the shifter housings for $50 or so and some will even install them while you wait (about an hour). Mine broke a few months ago and a local wrecking yard fixed it in an hour while I waited and charged me $115, which included the housing.
If you do it yourself, it will probably take you about 2 hours. All you need to do is drop the whole column about 8 inches (does not need to be removed from rig), unbolt the shifter (is on top of the column), bolt in the new shifter, then bolt the column back into place.