Short doors

We like to replace exterior doors (mostly just the front door) with regular house doors from HD or Lowes. They are way cheaper and better than the MH doors that you get from Blevins or other MH suppliers. If the exterior walls are tall enough you can cut a new rough opening and put in a normal 80 inch door. Problem is on many homes the exterior walls are too short for an 80 inch door. In the old days you could buy a wood exterior door and cut it down to fit the short opening. Now the doors are metal and I suppose you could cut them down but not preferred. Does anyone know where to order a shorter exterior prehung house type door that is a reasonable cost? Reasonable to me is approx $150 or less.