Yes, well I entirely agree with you. Notice too that supply components are also more expensive by size than most weapons and equipment! Build a supply tanker design, and it will cost more than most maxed-out warships! This only makes sense if you buy into some rationalizations and balance arguments, which are ok, but for those of us who think "an empty fuel tank" should be cheap, there are mods!
See
Proportions for a mod that makes supply components cheap and useful.
PvK