Keep in mind that the $30k GNX in 1987 is equivalent to nearly $63k (inflation method) in 2014 dollars. Car prices haven't kept up with inflation, though, so I predict $50-$55k.
According to Car and Driver, it depends on the car. They showed cars from around 1985 to now, price adjusted for today's dollars, and most of them cost more now. That would mean that they have exceeded inflation. There were examples of cars that sell for less now but that list was short:
The other thing to keep in mind with how car prices "haven't risen" is that we're getting much more for our money. Power locks & windows are 99% standard in the US. Radios and AC aren't options like they used to be. Emissions are way down. New cars aren't only "flat" when it comes to price, the products are much better too.
You gonna look at Chrysler's Hellcat offerings and just take it? They resurrected the "insane power, normal car" muscle car formula. Take your almost-but-not-quite SS, give it a Buick badge, the Z06 engine, paint it bright yellow with thick black stripes, and nuke the Hellcats with the rebirth of the GSX. Doooo eeeeet.
I just don't think GNX is the right nameplate to compete with the Hellcat, but GSX is. The SS is a far better car than the SRT-8 Charger (or any Challenger), so I'd argue a 700hp SS would have to be more expensive than a Hellcat. And frankly if you are making a 700hp burnout machine, does anyone really care about razor sharp responses? GM doesn't have a lame platform they can insert insane horsepower into. The Challenger was so perfect for the job, it's ridiculous. It's big, imposing, comfortable and fast. There's nothing you can build on Alpha that can compete with a 700hp 4400lb cruiser. It's not that kind of platform. You know, because it's actually a good platform.
I could see the GSX going after the Hellcat. "GSX was Buick's answer to Pontiac's GTO Judge and Oldsmobile's 4-4-2 W-30." - Wikipedia
The Judge was I would say very comparable to the Challenger and Wikipedia also states that the GSX was made to go after the Hemi Cuda.
I agree that the GSX would go after the Hellcat, but, I don't see Buick as the right GM brand to go after the Hellcat. That should be Chevy's job.
Either Bring back a Monte Carlo, or Chevelle (Honestly, the Chevelle is the most obvious choice to attack the Hellcat), or make a drag ready Camaro (Hello, ZL1?) to go after the Hellcat.
I still think Buick should go after Asian sport/Luxury (GT-R, NSX, etc.) since it is kind of luxury, and is a better American fit (turbo, possibly AWD) to go after the High end Asian Super Cars.
Chevy is the redneck muscle brand, let them handle the Hellcat. Chevy, what are you waiting for. The new Mustang Shelby 350 is looking serious, and there is no response to the Hellcat. Seriously, the ZL-1 doesn't really have a specialty, and it shared the same drive type as the Hellcat, Turn It UP!
Future Camaros could be SS vs GT, IROC (1LE but not a SS package, a real car name for the track, like the Boss) vs Boss/350GT, ZL1 vs Hellcat/GT500, Z-28 - full on track car. (If they even make it again...)
I would give you GSX, as I think the Challenger really fills a pretty nostalgic void that way. But not GNX. GNX was way too high tech (as a muscle car).