But biz will be half empty or more at full price, so it gets filled with upgrades of coach tickets to reward frequent fliers or full-fare users. The average has to be lower. The biz price may also be optimistic. United EWR-LHR is more like your $2.5k-$3k. Delta has an ATL-LHR option for first/business class with a bed that's more like $8k-$10k, and their Premium Select, which is more like United's business class, is $2.5k. Interestingly, they offer more beds than big seats.

I remember pricing out the Concorde years ago, before it was grounded. BA's first class subsonic was $8k, Concorde was $12k. (2001 dollars) If you're paying those rates anyway, it might be worth it to go faster, if you don't mind the relatively small seat and limited food service. Coach was $400-$600.