Suggestion: (improvements - added features)
When you post an item [left shift + LMB] in the Trade section, there should be automatically an option, the way to insert a 3-4 digit number, then press ENTER key to post that item with a price tag.
The Trading Section should be split into two categories. Example: WTS: [Want To Sell] [‘Singularity Cannon’ blueprint R13-15] and WTB: [Want To Buy] [‘Singularity Cannon’ blueprint R13-15].
Example: (Price tags should be mandatory!)
WTS: [‘Singularity Cannon’ blueprint R13-15] [price field - 3-5 digits] or 
WTB: [‘Singularity Cannon’ blueprint R13-15] [price field - 3-5 digits] or 
By posting in WTS or WTB section, people will not just know what you want to get, they will know if you’re selling or buying, they will know your asking or selling price.
If you already posted an item by the Post command, then this item’s price will also automatically be displayed, without you typing it, under WTS or WTB section. Just select it and press ENTER.
Optional: (added suggested price - suggested price range)
We got the minimal price and the best price.
Minimal price is really obvious - the bare minimum that you have to pay.
Best price is a random price that anyone can put.
I suggest adding suggested price range (from-to) as a means to stabilize the Trading System, thus reducing the number of preying rip-off or exploitative traders on unsuspecting victims.
This ‘Suggested item cost’ field should be added below 'Minimum item field.