It's possible, but would be better to put the average price under the item box so you don't have to edit the wiki templates.
Below is a sample item with the area to add your text bolded.
Quote:
<onlyinclude><includeonly><div class="hbdiv">[[Water Flask]]<span class="hb">{{Itembox
|itemname = Water Flask
|lucy_img_ID = 584
|statsblock =
QUEST ITEM<br>
This is a drink!<br>
WT: 0.4 Size: SMALL<br>
Class: ALL<br>
Race: ALL<br>
}}</span></div></includeonly></onlyinclude>
{{Itempage
|notes =
|itemname = Water Flask
|lucy_img_ID = 584
|statsblock =
QUEST ITEM<br>
This is a drink!<br>
WT: 0.4 Size: SMALL<br>
Class: ALL<br>
Race: ALL<br>
|