My impression here, is that, like with many other parts of the game, the devs did not think it through, or even tested it once, or they would have  noticed how bad it is.

This is not simply about putting a wrong price tag on something by simply using arbitrary numbers without thinking or testing,
but ruining an actually "nice" feature, that would help players bond with the game emotionally (you have no idea how important that is!), and turning it into a dissapointment for all the casual and yet low and mid lvl players, adding just a slight bit to the chance that they won't continue playing for long, won't recommend it to friends, won't bring their friends, which all, in the end, results in less profit, less money for further developement... you get the idea.

On another note, the current customization implementiation is very lacking!

How should it be? ... in that you can define one "personal" style per item type, and apply that for little cost, slighting increasing maybe with level, instead of having to put together everything manually again and again.
If you found something you like, you will likely replace that type of item with the same item type of higher levels,
we have 2018 already, there is NO NEED to customize every items again and again BY HAND, seriously!

The only thing that should still be on a per item base should be the "change the item tier"-visuals, I guess.

They should really chenge that mechanic so you keep the purchased colors on every armor (or other visible item) you change to. Yes, it's not realistic, but I guess more people would run around colored.