I have ALWAYS known they're expensive, but as you yourself said, five figures is a lot for bass.
That it is, and to be honest (and NOT wanting to open a can of worms) I have questions myself about how "Brand X" can charge so much for say, a fairly simple bolt-on bass.
In the case of Alembic, the electronics are very sophisticated, along with the hardware, woods, etc. so you might ascertain that as you spec a build... ** KA-CHING!*
And besides the first-quality elements of the instrument itself, Alembic has a one-of, illustrious name and legacy.
Gotta pay for that too!
Wish I could throw a (imaginary) few in my (imaginary) Lambo!