The prices of similar (if not down right better) GM cars are simply not all the same. Chevy will ALWAYS be the higher priced one of the bunch, period. They always have been, they always will be.
It makes no sense to me either. I sold my 65 Skylark a year or so ago. It was VERY nice with zero rust, EVER. The body bolts were still bore the original zinc plating! The underside of the floor was shiny original body color! Just a nice old car perfect for restoration. Drove it everyday, I would still run off across country in it. 2Dr hardtop with bucket seats.
I put it on ebay and got $2700 for it. It made me want to cry that if it was a Chevelle in the same condition it probably would have gotten eight or ten grand!
But that is just the way it is, even if it is better (and I believe the Skylark was) than the Chevelle, there are fewer people who wanted it.
Supply and demand my friend, supply and demand.
Brian