Here is an article on the prices, seems like prices for domestic travel have fallen somewhat (about 25%) since the 60s. That is comparing economy. So if you compare business now to economy then I think the price has probably increased dramatically.
From everything I read, people don’t pay for business for the most part.
Meaning when a business class seat is purchased, it’s usually a reimbursable seat paid for by a company (unless you travel on behalf of the “frugal” FAANG - ask me how I know).
Other times, the seat is a free upgrade perk for people with status or the right card.
Honest question though, what is “business class” these days? Delta has basic, main, comfort+ and first.
I just started flying American so I haven’t paid any attention to it.
https://simpleflying.com/50-years-airfares/