It would be nice if this could be implemented but fooling people or rather use peoples' laziness to your benefit might not be a bad idea after all... I've done this many times as many times i've wasted my gil on stuff that could be bought from vendors half or less price.

This case rests mostly on the crafters' side where you need many different materials. Imagine if you have to travel to, let's say, 4 different regions to buy stuff rather than waste 10k-20k more to buy them instantly. Many people are just too lazy to do this, simple as that. However, for "expensive" stuff there are certain ffxiv sites that mention where you can buy and for how much.
I don't think its just a waste of time to do a bit of research before you buy after all...