Good reference images if anyone needs them:
Image 1, Image 2.
I can already tell you that your price limit is definitely not going to conform with a price that many commissioners are going to give you for the total cost for this coat.
...I have commissioner recommendations in mind for you but since I have worked with these people before, I can tell you right now that they would not be able/willing to make exactly what you are asking for for such a low price.
I say that based on what you said here alone:
The aim is to have a costume which nearly replicates the look and feel of the original character design when it comes to materials, quality and details.
When asking for screen accuracy or anything near it, that on its own already says that your commission is going be over 300 Euros.
So I wanted to ask you guys if there is some commissioner you could recommend me for doing this for a reasonable prize that has the experience needed for making such a good costume with better materials like cotton and wool.
That could easily be a base price for some...especially with what you are wanting to be made.
Arno's costume is very, very detailed and since you are wanting to be specific...you're going to pay a large sum of money for this piece.
If/When you want screen accuracy with any
costume being made, you've got
to be ready to pay for it because there is no commissioner that is going to work hard to nearly make a replica of something for cheap.
Since you say that you are totally new to cosplaying and everything, you may want to read this Thread that I made called Commissioning 101 because there are a lot of things that people don't consider when they're totally new to this stuff:
This is a direct link to the Thread!
Also, if you mentioned the fact that your price limit was 300 Euros, the first thing that would probably be done is using cheaper materials because that would definitely cut down on the price.
Another thing: unless you are wanting to wear this coat strictly when it is cold, you may want to use other materials anyway because you may get a bit warm...which only leads to being uncomfortable and sweaty in your costume.