They are slightly cheaper today in regards to buying power, however Apple has come a long way since 2004 and refined its manufacturing processes and reduced costs. I would expect the 2016 MBP it to be cheaper then what it is now.
They can be cheaper, but people are willing to pay the price which is why Apple's hardware margins are the envy of the industry.
As for old tech prices, my most expensive computer was a 1989 HP Vectra RS/25c workstation at $25,000.