Good morning,
Using
https://www.bankofengland.co.uk/monetary-policy/inflation/inflation-calculator
£45 in 1976 was worth £121 in 1988 and I paid around £250 for a Raleigh Record Sprint at that time, that £250 is now £685.
The Record Sprint was 501 and lots of alloy components so double a Puch Alpine seems about right.
Currently a Specialized Allez with Claris is £799 or £100 more than a Record Sprint.
The Record Sprint would have had a made in the UK frame with some other parts from similar high cost countries and some from lower cost countries. Isn't the Allez entirely built in locations where costs are carefully monitored?
In terms of spec, the Allez is aluminium alloy quite intensively shaped compared to a "commodity premium" steel tube hand welded, I am pretty sure that my Record Sprint was hand made in Britain,,,,, it broke after a few thousand miles.
The rest of the components seem similar excluding STI/down tube shifters, but the price difference when new is a lot less than as retail packaged spare parts.
The Decathlon\Halford Carrera range do seem to have some parts that I would put as slightly lower spec than the Record Sprint but many now have disc brakes, plus of the course a discount for not being a premium bike brand.
A Carrera Vanquish at around £450 has mechanical discs and Alloy frame with CF forks, are these improvement or just changes and weighs about 3lbs less than the Record Sprint, on the other hand a lot of the minor parts do seem to be lower spec.
So it seems that prices don't seem to have changed that much if you try and compare like to like spec wise, as far as that is possible.
Bye
Ian