I found a few boxes of American Eagle 40gr that I purchased around 2000-2003. The pricetag said $1.49 for 50 rounds, which is right in the ballpark of that stuff from 1981.
This raises an important point about prices. Inflation isn't the whole answer. It may have become cheaper to manufacture 22lr in those 20 years. That Ruger 10/22 was certainly a bargain by today's standards. I bought a 10/22 around 2002 and it cost almost exactly the same in 2019 before the panic started. In that case, there was very little inflation over that 18 year period and very modest growth in wages. I bet Ruger found ways to make the same rifle cheaper to counteract increases in production costs, or maybe their margins went up.