Median wage in 1972 was about $7,000, so either of those cars cost about 65% of an average years wages.
1972 Plymouth Road Runner
Base Price................................ 3800
GTX Option {Code E86}............. 161 < Yes
Air Grabber 'Cold Air Package'..... 68 < Yes
Power Steering............................ 90
Power Front Disc Brakes.............. 71 < Mandatory
4-Speed Transmission................ 208 < If you were serious
Automatic Transmission............. 230
Performance Axle Package........... 68 < A steal
Rallye Wheels {15"}.................... 60 < Unless Mags were in your future
AM Radio...................................... 66
Tinted Glass................................. 43
Tachometer.................................. 52
Decorative Exhaust Tips............... 25
Rallye Steering Wheel.................. 21
Hood Hold Down Pins................... 17