To adress the artistic problems of producing unique materials such as weapons or clothing...
The simple answer would be; Have you ever herd of a game called "Galactic Civilizations" >>>???
It has a ship design function that has basic, pre-set items, such as Tons of differnt pre-shaped objects that can inter-connect with eachother to create unique and different looking possibilities of ship presentations once you commit the Blue print.
That type of system would be the best to start a new idea like this. Create Hundreds - Thousands of different micro parts, that can be combined and designed to combine with other parts. Each part can have 1 or more positive and/or negative stat atributes to them, and depending on how you make it look, and which pieces you choose, you will create an absolutly unique and Individual item, that will maintain its own market value...
Players who create blueprints in this way, would be able to save their designs incase they want to create more blueprints for the items later. And The markets would only fluctuate towards good designs. The better and more sustainable/Economic a design, the more of them you will sell...
Of cource others could reverse engineer the items from observing their parts. But that could be tedious depending on the number and use of each individual part in each creation...
In essence, Each unique item would be the creators own cash cow if they design it well... Other players will WANT TO BUY IT!
P.S.
I know im using another game as reference. But you shouldnt be concerned with that. Because it is only adressed for the purposes of Improving this game... Please dont block this post.
P.P.S
Each individual micro part, would be craftable. Meaning if you overview a list of all available parts which you wish to use to create an item, You would either have to buy those pre-made parts from others. Or find a BP for them, and create those parts yourself.
In essence, Creating new and unique items, would entail alot of money, and concentration to develope just what you want. And if you cant afford it, you will get lesser items created by players with little capitol...
The market wouldn't crash, Unless we don't get creative people designing new items to promote more spending all the time. But Im really sure, that this world has no lack of creativity in it