Terminal rust can be categorized into 2 areas.
1. Not economically viable to repair
2. A bucket full of rust that use to be a car.

The mustang I'm working on at the moment really fell under the first category. The reason the owner wanted to rebuild it is due to it's rarity.

15 years ago, so many holdens were falling under the first category, but now that a little time has passed we find that they are worth spending the money on.

After market panels are getting better so we tend to use them a lot. They do require modifying but it's a lot less expensive than having to make a full panel from a flat piece of steel. Small patch panels are easy.

Most of it just comes down to the owner of the vehicle and how badly they want to assault their bank account.