Very difficult comparison to make though I have given it much thought myself. One simple way would be the consumer price index. If bike X cost $150 in 1970 it would cost $794.46 today for example. Then you see what models are available in that price range. Crude but it provides a starting place. I suspect though that bike prices have increased faster than inflation however. I mean did a top of the line full Nuovo Record, Columbus or Reynolds 531 bike cost $1400 in 1970? ‘Cause that’s what it would have had to cost to be the equivalent of today’s top end $7000+ models (maybe they did, I don’t know, I was but a wee lad back then but I doubt it – I’m thinking more like $500). Also, I think you will typically find that there are many more models today to choose from then back then when many manufacturers may have only had 4 or 5 models. Take a look at today’s BianchiUSA website. There are more bikes there then you can count.

I consider my 1972 Bottecchia Giro d’Italia to be the equivalent of today’s Bottecchia BS 815 8avio or a maybe a Bianchi 1885 - Carbon Centaur (neither available stateside) but those are certainly arbitrary comparisons based on where the bikes fit in the manufacturers lineup or among other bikes generally. In my case I would look at the top end frame on the Giro (hand made from double-butted Columbus tubing, same as the top of the line Professional) but with a lower end set of components (not a group really since it’s a mish-mash of stuff) that I would compare to Centaur or Ultegra in today’s market.