Value of muscle cars in the 80's?

Let's say you wanted to buy a rare muscle car that's worth about 45 grand nowadays like a '70 Plymouth Cuda 440 in 1987... How much did they cost approx. back then? I'm talking about cars such as a '70 Olds 442 455, a '70 El Camino SS 454, a '69 Mustang Mach 1 428 CJ, etc.