You can order a custom made door that size, but it will cost you double if not triple the cost.

When faced with these situations I modify the steel doors in the field, by taking the head off and cutting the door to the right size, adjusting the top of the door jambs, and re-attaching the head back on.

Most carpenters or door installers know how to do that with metal exterior doors, just make sure they did that in the past and know what they doing, because I've seen hacks cutting the bottom of the door, leaving the door without factory installed sill, or cutting the top of the door to short, etc

Would a solid wood door be cheaper to cut down to size?

If you doing it yourself the difference in the cost will be only the difference in the cost of the door. As cutting goes for the metal door you would need a good quality carbide blade or a metal blade and for the solid core wood door, you can cut with most wood blades... In bost cases apply tape to the face of the door.

Thank you for all your comments. Mark