I am still not sold a nice interior will drive up costs that much. Lets say the base car costs 45000 dollars. Now, this is a complete car. Lets say we all agree that the suspension, boat anchor pushrod engine (had to get that in their, lol), and exterior are fine the way they are and all we have to change are seats, steering wheel, and dash.
Having said that, we have already spent the money on the existing seats, steering wheel, and dash. So out of the 45000, lets say the seats, steering wheel and dash account for 5000 dollars, I doubt it, but lets go with that math. So the only increase would be the DELTA cost between the old stuff and the new stuff. I would bet you could get a hell of a big improvement for 2500 dollars more. Especially if you left the design alone and just improved the tech, and material quality.
So in a nutshell, you could drastically alter the cabin of the Vette without making the base vette jump from 45k to 80k.
There I am done, make me CEO of GM and I will make it so..