Print paper was cheap then, too. In the early - mid 70's, I regularly paid $9.95 (retail) for a 100-sheet box of 8x10 Polycontrast F. It wasn't cost-effective to buy smaller sizes or smaller packages. I regret not being more insistent that my dad teach me to shoot large format, since he had both 4x5 and 8x10 cameras, and I was gifted a 5x7 by a retired photographer for whom I did odd jobs. One of many missed opportunities.
In December 1971, silver was $8.67 per ounce. In January 1980 (thank you, Hunt Brothers), silver spiked at $118.55 per ounce. Price dropped pretty rapidly after that, but Kodak and the others didn't see much of a reason to adjust their prices for finished goods.