Well, if a S30 were to be fabricated in aluminum, or custom built up from scratch, it could be 'upgraded'. Stiffer chassis, longer rails, perhaps a Gnose like front end, wide body as well, and just overall better aero. That would be interesting to see.
If the S30 interior bits would be used - or even 240SX / Z32, which seem to fit with some work - dash etc, I wonder how far down the price could be kept. They do make tube frames for replicars like the Cobra for decently low prices, but I think that a quality package might edge closer to that of the Noble M400 price. The Noble rolling chassis is around $75K, and the Factory Five kits look to be starting at $20k. Wonder where a good S30 [re]design would fall. Just need a market with enough demand and money to back it up with.