Let's say that on Jan 1, 1970, you took your pre-1964 quarter and pulled out the 6.25 grams of silver in at the price of $12.37 a troy ounce. You'd get $2.48.
If you put that $2.48 in a money market earning just half the fed discount rate for the last 47 years, it'd be worth $7.99 today. The silver would be worth $3.37. (The currency would likely be a lot more that $7.99, because the difference between money market rates and fed discount rate historically hasn't been as high as the very conservative 50% markdown I used here.)
There are a lot of moving parts in an economy that affect cost of living. A lot of stuff has changed since 1970 beyond going off the gold standard. Massive productivity changes, energy and raw material price shocks, demographic changes, policies and laws changing behaviors all across the individual and business landscape. It's difficult to isolate one individual factor as the sole cause.