JFK-LHR-JFK business class is about $9k assuming you're travelling fairly flexibly without a Saturday night away, at least pre-covid.

Even a month away I can't see a direct flight for less than $8k return leaving JFK evening of Jul 11th and returning July 16th.

The flights are pretty much empty at the moment, but they would be at any price. Doesn't mean that VS/DL will sell for $7k (undercutting BA/AA's $8k), it's effectively a cartel.

First of all, don't be surprised if a goal of “the cost of a business class ticket” translates into something like 50% or 100% more.

Also the Concorde was not that much of a premium over first class on, say, a 747. I'm remembering +30% or +50%. Of course, that first class ticket was very expensive if you inflate it to today's money.