$8K is a normal RT JFK-LHR ticket today in business class. This is vs $800 in economy. However, Boom proposes that the same $8K can support economy-style seating traveling at Mach 2.2 instead of mach .80. It does not seem unreasonable to me that 3x the speed will cost ~10x as much.
People who have worked in computing all their lives will have seen multiple "magic 10x improvement" cycles, so might have an implicit believe that it will happen everywhere.
But one should not assume that this will happen for the task of pushing big metal tubes through the air by burning things. The physics of it is not on the side of easy 10x improvements in that case.
And remember that both BA and Air France got their Concordes “for free”
Technology does enable 10x improvements over half a century sometimes.
In reality, fleet average fuel economy has been nearly flat for four decades, with the biggest periods of movement being driven by brief excursions in the price of crude oil. Those efficiency excursions were in turn driven not by technological improvement, but by changes in the makeup of the vehicle fleets themselves (lighter cars, smaller engines).
https://en.wikipedia.org/wiki/Corporate_average_fuel_economy
Also note most aircraft capable of supersonic cruise nowadays don't use turbojets, they use low-bypass turbofans (mostly around 0.3:1).
If you want to go the same distance for 1/10th the cost, you need to use 1/10th the fuel, have 1/10th the maintenance overhead, and have 1/10th the staffing cost all at the same time.
You can't go over 100% efficiency in any area, so to see 1/10th the cost you would need the entire aircraft industry in the 1970s to be operating at under 10% efficiency, a low bar I am highly skeptical of.
It's not like Aeronautics engineers or the Airline industries were gorillas banging rocks together with no understanding of what they were doing, and I find it hard to believe there is enough room for a 10x increase in efficiency from the 1970s even with a perfectly efficient aircraft and airline behind it.
But hey, if you really believe it's possible, invest in Boom because they must have designed a cold fusion reactor running on tap water to power their jet and everyone who invests will probably become a trillionaire overnight once they reveal it.