Honestly the only reason some of those boosts cost so much is because of cult-like hype and consumer herd mentality. There are many other types/instances of pedals where a high price is completely justified by the complexity of the circuit, the quantity or cost of the parts, or the sheer quality of construction. But with those super-expensive boost pedals, there is no complexity, few parts, the parts are commonplace and cheap, and most of the makers' claims about construction quality are utter bull. They'll say "made with only the finest Alpha pots, precision resistors, and indestructible cast-metal housing" and it's all garden-variety cheap pedestrian stuff really. All hype, and consumer mania to have "only the very best" on their pedalboard.
Again though there are meritorious exceptions, I am not throwing all boosts or boost builders under the same bus.