Well, I came up with the perfect solution. Found 2 car-guy neighbors who were enthusiastic about a joint purchase of a good plasma cutter. It's on the way, none of us will use it more than a couple of times a year, but at 1/3 the total purchase cost, it makes this luxury item more justifiable (and, I only have to store it a third of the time!)
Certainly I'll use some of the other tools in my arsenal for rusty frame/floor pan removal: power sheet metal cutter, air hammer/drill, cut off tool, etc, but I can sure see where only that plasma cutter will be able to get into some tight places and make the clean cut I need to do a good job. Life is good!
As the joint-ownership thing seems so obvious, I find myself wondering why so few car marque clubs (at least in Austin) don't do some of the same stuff... club purchase of a few expensive pieces of equipment that members can borrow seems to make a lot of sense, but it doesn't seem to happen very often.