Not that this really justifes anything.
Tub amps tend to be very simple designs (there is a lot of subtlety in the details), so more expensive deigns have better power supplies and better overall component quality.
To see how deep that rabbit hole goes go look at the audionote catalog, and see what they will charge you for a single capacitor or choke.
In more expensive tube amps a LOT of the cost is in the power supply.
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