Quality Level of mats has no effect on end price of item.
Infact, the Choice, Excellent or Supreme level of Quality level mats seems to have little effect on price of item.
The only thing anyone seems to care about is the damage and hits, armour protection level and smash, pierce, slice protection and if the amp was made using pha amber...
Heres the problem:
A Q50 Weapon made from Q250 Mats at Supreme level from the best type of mat usable in making it, is technically worth the exact same amount of money as a Q250 Weapon. Who will pay 500k for a Q50 amp tho?
Now from a harvesting point of view there is no point making a Q50 weapon from Q50 mats, as the harvester gets no xp getting these mats.
Pricing, can certainly be based on the type of mat being used on construction, but since people only want the very best we can make, most mats are ignored. Why buy a longsword made from perfling if you can get one made from oath.
Similar a Crafter wont buy lower spec mats to make weapons, armour etc they only buy the best and try to get them at the lowest price. They will then try to sell the item for the maximum possible.

And Harvesters will only harvest the best they know of in quantity to sell them.
All other mats are used for skilling up leveling.
So whats to be done? Standardise prices? no chance this will happen, some people will say its a good thing and others will say price fixing is cartel and so on.. How do you set a price for an item thats made at lvl 50 using mats that can make any weapons from q50-q250? how do you do that?
all this is without getting into how long the item lasts...