I don't think it's the case if you take inflation into account.

You could see here: https://www.reddit.com/r/dataisbeautiful/comments/16dr1kb/oc...

new ones are generally cheaper if adjusted for inflation. This is a sale price, but assuming that margins stay the same it should reflect the manufacturing price. And from what I remember about apple earnings their margins increased over time, so it means the new phones are even cheaper. Which kind of makes sense.