Maybe someone with internet skills can compare the 1970 price of a C172 to a similarly priced BMW or Mercedes or John Deere tractor, and recompare the difference to equivalent plant today.
I'll give it a shot.
The 1971 C172 Skyhawk (according to Wikipedia) retailed for $US 14,995.
A new C172, admittedly with glass cockpit avionics and other gadgets, but new from the factory and ultimately doing the same job of transporting two adults and two midgets in moderate discomfort, is listed online from Textron for $US403,000 or so, or roughly 26 times the price of the 1971 model. That works out to just shy of $520,000 Australian dollars today, before you put fuel into the tanks.
The Mercedes 280 SL, which was just what appeared when googling 1971 Mercedes sports car, and apparently was (and remains) a fairly highly regarded sports car, had a new retail price of ~$11,958, just under the price of some of the slightly older C172s, and a new Mercedes sports car, depending on the trimming and model, won't give much change out of $100,000.
A top of the line 1971 Ford Mustang had a sticker price of $US 4124, the new top of the range Ford Mustang comes to around $US 55,000
And in 1971 the US median household income was $US 7956, compared to today- the latest figures I could quickly find were from 2014, $US 53013.
So for a rough guide from 1971 to today, the other equivalent items have gone up roughly ten times in price, looking solely at the number of US dollars being handed over, and the average Australian weekly income went from around $88 per week - $~4580 per year - to around $1145 after tax.
A C172 went from less than two years of average US income, to more than 7 years of average US income, or less than three years of average Australian income to just under 9 years of average Australian post-tax income. If you want a Mercedes, Ford Mustang, expensive yacht or some other luxury toy, you can do it much more affordably than going anywhere near a Cessna, and have $300,000 left in the bank. And on the weekend you can take your car or yacht for a fun drive without checking your medical, licence, ASIC, biennial flight review, night currency, $1400 headset, stopping off to buy new maps and ERSA because the old ones expire every 3-6 months, updating your AIPs, putting $300 in the bank to cover fuel and maintenance for every hour in the air and so on and so forth.
There are probably some minor rounding errors in there, but the gist of it remains:
Ford Mustang, takehome pay, Mercedes sportscar etc are approximately ten times their 1971 prices. The Cessna, 26 times.