Yes, math in the NMS universe is terribly confusing as they never seem to have developed an equivalent to SI-norms.
Still easier than imperial units, though…
In any case, units for distance and for money obviously aren’t the same. At least they measure time in seconds, otherwise speed would have to be written as units per unit, which might actually be worse than the imperial system. The base value of pretty much everything is noted when you hover your mouse over it in the inventory.
I’m not quite sure how that relates to the galactic average, since that seems to be a little higher than the base value. In any case, you can only sell stuff below the galactic average. Noone will pay above that price, with the exception of specialised trade goods that can’t be crafted.