For the record, a precious few old muscle cars will fetch money like this. There are plenty of absolutely mint, kickass muscle cars you can get for 20-40 grand. The ones that fetch big money are the ultra rare, most desirable package, original (not replacement panels) cars like a Hemi Daytona in mint, non-restored condition. Something like a transmission and seat option, or some option package, can make a difference of 100k+.
I'm not saying that these cars are overpriced, only that the collector car market is a very strange beast. People try to put some kind of method to it but what it really comes down to is having 2 or more rich guys who have a boner for this exact car because they couldn't have one back when they were poor. They drive the price up, trying to outbid one another, and the one to give up last, gets it and that's what it's "worth". Like the 300SL Gullwing... it's really a pretty crappy car but back in its day, it was the car you dreamt about owning because in your mind, it guaranteed to get you any ass you could want. So they sell for millions.