You're mistaken. $43 gets you a roller, not anywhere near a finished product. By the time you customize a few things and fix some of the stupid things the factory did, coupled with drivetrain installation, do the body fit/finish, interior trimming, electrical wiring, fuel stuff, etc, you have a lot more time and money into it.
If you haven't built a kit car, no matter which company, Superperformance, etc, then you tend to believe some of the idiots that say you can slap together a car in 120 hours. Sure, it can be done, but it looks like $hit. That's OK with some folks.
As far as your comment about the GTM, it's entirely subjective of course. Let me put it another way. I've DRIVEN both a Factory Five GTM and a Superlite Coupe. Not on a track, but around town. As with anything, ride quality depends on dampener choice and wheels/tires. Unless you're an expert that will extract more than 50% of each car's potential, preference just boils down to what you like in design and fit/finish.
I didn't go with either of these because of the poor market on getting rid of my NSX. It's far cheaper and almost as satisfying just to spend $20k on the NSX looks and performance than sell it and build a car.
If you want an SLC and have the means, I would certainly do it!
My $0.02.
Dave