I think you have to wake up and smell the coffee
Cap1 
Well, it's the same as it always was "at the time". The basic crapy model was cheap, the high perf one was high $$$.
1967 Mustang coupe $2,461
1967 GT350 $3,994
1967 GT500 $4,195
1967 Super Snake was planed for $7,500, but only one ended up made out of 50 planed.
That kind of follow today's figures of $23K base v6, $28K GT, $33K Shelby GT, $40K GT500, $80K 715HP Super Snake.
I bet you can find similar price jumps between a 1971 V6 Challenger, and 71 Challenger R/T six pack, or a 1969 Camaro with a straight 6, a 1969 396 RS/SS, and Yenko Camaro.